announced the judgment of the Court and delivered the opinion of the Court with respect to Parts I, III, and IV, and an opinion with respect to Parts II and V*

The questions presented are whether Terry Williams’ constitutional right to the effective assistance of counsel as defined in Strickland v. Washington, 466 U. S. 668 (1984), was violated, and whether the judgment of the Virginia Supreme Court refusing to set aside his death sentence “was contrary to, or involved an unreasonable application of, clearly established Federal law, as determined by the Supreme Court of the United States,” within the meaning of 28 U. S. C. § 2254(d)(1) (1994 ed., Supp. III). We answer both questions affirmatively.

I

On November 8,1985, Harris Stone was found dead in his residence on Henry Street in Danville, Virginia. Finding no indication of a struggle, local officials determined that the •cause of death was blood alcohol poisoning, and the case was considered closed. Six months after Stone’s death, Terry Williams, who was then incarcerated in the “I” unit of the city jail for an unrelated offense, wrote a letter to the police stating that he had killed “'that man down on Henry Street’” and also stating that he “'did it’” to that '“lady down on West Green Street’ ” and was “ 'very sorry.’ ” The letter was unsigned, but it closed with a reference to “I cell.” App. 41. The police readily identified Williams as its author, and, on April 25,1986, they obtained several statements from him. In one Williams admitted that, after Stone refused to lend him “ 'a couple of dollars,’ ” he had killed Stone with a *368mattock and taken the money from his wallet.1 Id., at 4. In September 1986, Williams was convicted of robbery and capital murder.

At Williams' sentencing hearing, the prosecution proved that Williams had been convicted of armed robbery in 1976 and burglary and grand larceny in 1982. The prosecution also introduced the written confessions that Williams had made in April. The prosecution described two auto thefts and two separate violent assaults on elderly victims perpetrated after the Stone murder. On December 4, 1985, Williams had started a fire outside one victim's residence before attacking and robbing him. On March 5,1986, Williams had brutally assaulted an elderly woman on West Green Street— an incident he had mentioned in his letter to the police. That confession was particularly damaging because other evidence established that the woman was in a “vegetative state” and not expected to recover. Id., at 60. Williams had also been convicted of arson for setting a fire in the jail while awaiting trial in this case. Two expert witnesses employed by the State testified that there was a “high probabil*369ity” that Williams would pose a serious continuing threat to society. Id., at 89.

The evidence offered by Williams’ trial counsel at the sentencing hearing consisted of the testimony of Williams’ mother, two neighbors, and a taped excerpt from a statement by a psychiatrist. One of the neighbors had not been previously interviewed by defense counsel, but was noticed by counsel in the audience during the proceedings and asked to testify on the spot. The three witnesses briefly described Williams as a “nice boy” and not a violent person. Id., at 124. The recorded psychiatrist’s testimony did little more than relate Williams’ statement during an examination that in the course of one of his earlier robberies, he had removed the bullets from a gun so as not to injure anyone.

In his cross-examination of the prosecution witnesses, Williams’ counsel repeatedly emphasized the fact that Williams had initiated the contact with the police that enabled them to solve the murder and to identify him as the perpetrator of the recent assaults, as well as the car thefts. In closing argument, Williams’ counsel characterized Williams’ confessional statements as “dumb,” but asked the jury to give weight to the fact that he had “turned himself in, not on one crime but on four . . . that the [police otherwise] would not have solved.” Id., at 140. The weight of defense counsel’s closing, however, was devoted to explaining that it was difficult to find a reason why the jury should spare Williams’ life.2

*370The jury found a probability of future dangerousness and unanimously fixed Williams’ punishment at death. The trial judge concluded that such punishment was “proper” and “just” and imposed the death sentence. Id., at 154. The Virginia Supreme Court affirmed the conviction and sentence. Williams v. Commonwealth, 234 Va. 168, 360 S. E. 2d 361 (1987), cert. denied, Williams v. Virginia, 484 U. S. 1020 (1988). It rejected Williams’ argument that when the trial judge imposed sentence, he failed to give mitigating weight to the fact that Williams had turned himself in. 234 Va., at 181-182, 360 S. E. 2d, at 369-370.

State Habeas Corpus Proceedings

In 1988 Williams filed for state collateral relief in the Danville Circuit Court. The petition was subsequently amended, and the Circuit Court (the same judge who had presided over Williams’ trial and sentencing) held an eviden-tiary hearing on Williams’ claim that trial counsel had been ineffective.3 Based on the evidence adduced after two days of hearings, Judge Ingram found that Williams’ conviction was valid, but that his trial attorneys had been ineffective during sentencing. Among the evidence reviewed that had not been presented at trial were documents prepared in connection with Williams’ commitment when he was 11 years old that dramatically described mistreatment, abuse, and neglect during his early childhood, as well as testimony that he was “borderline mentally retarded,” had suffered repeated head injuries, and might have mental impairments organic in origin. App. 528-529, 595. The habeas hearing also revealed *371that the same experts who had testified on the State’s behalf at trial believed that Williams, if kept in a “structured environment,” would not pose a future danger to society. Id., at 313-314.

Counsel’s failure to discover and present this and other significant mitigating evidence was “below the range expected of reasonable, professional competent assistance of counsel.” Id., at 424. Counsel's performance thus “did not measure up to the standard required under the holding of Strickland v. Washington, 466 U. S. 668 (1984), and [if it had,] there is a reasonable probability that the result of the sentencing phase would have been different.” Id., at 429. Judge Ingram therefore recommended that Williams be granted a rehearing on the sentencing phase of his trial.

The Virginia Supreme Court did not accept that recommendation. Williams v. Warden, 254 Va. 16, 487 S. E. 2d 194 (1997). Although it assumed, without deciding, that trial counsel had been ineffective, id., at 23-26, 487 S. E. 2d, at 198, 200, it disagreed with the trial judge’s conclusion that Williams had suffered sufficient prejudice to warrant relief. Treating the prejudice inquiry as a mixed question of law and fact, the Virginia Supreme Court accepted the factual determination that available evidence in mitigation had not been presented at the trial, but held that the trial judge had misapplied the law in two respects. First, relying on our decision in Lockhart v. Fretwell, 506 U. S. 364 (1993), the court held that it was wrong for the trial judge to rely “ ‘on mere outcome determination’ ” when assessing prejudice, 254 Va., at 23, 487 S. E. 2d, at 198 (quoting Lockhart, 506 U. S., at 369). Second, it construed the trial judge’s opinion as having “adopted a per se approach” that would establish prejudice whenever any mitigating evidence was omitted. 254 Va., at 26, 487 S. E. 2d, at 200.

The court then reviewed the prosecution evidence supporting the “future dangerousness” aggravating circumstance, reciting Williams’ criminal history, including the sev*372eral most recent offenses to which he had confessed. In comparison, it found that the excluded mitigating evidence— which it characterized as merely indicating “that numerous people, mostly relatives, thought that defendant was nonviolent and could cope very well in a structured environment,” ibid. — “barely would have altered the profile of this defendant that was presented to the jury,” ibid. On this basis, the court concluded that there was no reasonable possibility that the omitted evidence would have affected the jury’s sentencing recommendation, and that Williams had failed to demonstrate that his sentencing- proceeding was fundamentally unfair.

Federal Habeas Corpus Proceedings

Having exhausted his state remedies, Williams sought a federal writ of habeas corpus pursuant to 28 U. S. C. § 2254 (1994 ed. and Supp. III). After reviewing the state habeas hearing transcript and the state courts’ findings of fact and conclusions of law, the federal trial judge agreed with the Virginia trial judge: The death sentence was constitutionally infirm.

After noting that the Virginia Supreme Court had not addressed the question whether trial counsel’s performance at the sentencing hearing fell below the range of competence demanded of lawyers in criminal cases, the judge began by addressing that issue in detail. He identified five categories of mitigating evidence that counsel had failed to introduce,4 *373and he rejected the argument that counsel’s failure to conduct an adequate investigation had been a strategic decision to rely almost entirely on the fact that Williams had voluntarily confessed.

According to Williams’ trial counsel’s testimony before the state habeas court, counsel did not fail to seek Williams’ juvenile and social services records because he thought they would be counterproductive, but because counsel erroneously believed that “ ‘state law didn’t permit it.’ ” App. 470. Counsel also acknowledged in the course of the hearings that information about Williams’ childhood would have been important in mitigation. And counsel’s failure to contact a potentially persuasive character witness was likewise not a conscious strategic choice, but simply a failure to return that witness’ phone call offering his service. Id., at 470-471. Finally, even if counsel neglected to conduct such an investigation at the time as part of a tactical decision, the District Judge found, tactics as a matter of reasonable performance could not justify the omissions.

Turning to the prejudice issue, the judge determined that there was “ ‘a reasonable probability that, but for counsel’s unprofessional errors, the result of the proceeding would have been different.’ Strickland, 466 U. S. at 694.” Id., at 473. He found that the Virginia Supreme Court had erroneously assumed that Lockhart had modified the Strickland standard for determining prejudice, and that it had made an important error of fact in discussing its finding of no prejudice.5 Having introduced his analysis of Williams’ claim *374with the standard of review applicable on habeas appeals provided by 28 U. S. C. § 2254(d) (1994 ed., Supp. Ill), the judge concluded that those errors established that the Virginia Supreme Court’s decision “was contrary to, or involved an unreasonable application of, clearly established Federal law” within the meaning of § 2254(d)(1).

The Federal Court of Appeals reversed. 163 F. 3d 860 (CA4 1998). It construed § 2254(d)(1) as prohibiting the grant of habeas corpus relief unless the state court “‘decided the question by interpreting or applying the relevant precedent in a manner that reasonable jurists would all agree is unreasonable.’ ” Id., at 865 (quoting Green v. French, 143 F. 3d 865, 870 (CA4 1998)). Applying that standard, it could not say that the Virginia Supreme Court’s decision on the prejudice issue was an unreasonable application of the tests developed in either Strickland or Lockhart,6 It explained that the evidence that Williams presented a future danger to society was “simply overwhelming,” 163 F. 3d, at 868, it endorsed the Virginia Supreme Court’s interpretation of Lockhart, 163 F. 3d, at 869, and it characterized the state court’s understanding of the facts in this case as “reasonable,” id., at 870.

We granted certiorari, 526 U. S. 1050 (1999), and now reverse.

II

In 1867, Congress enacted a statute providing that federal courts “shall have power to grant writs of habeas corpus in *375all cases where any person may be restrained of his or her liberty in violation of the constitution, or of any treaty or law of the United States .. .Act of Feb. 5, 1867, ch. 28, § 1,14 Stat. 385. Over the years, the federal habeas corpus statute has been repeatedly amended, but the scope of that jurisdictional grant remains the same.7 It is, of course, well settled that the fact that constitutional error occurred in the proceedings that led to a state-court conviction may not alone be sufficient reason for concluding that a prisoner is entitled to the remedy of habeas. See, e. g., Stone v. Powell, 428 U. S. 465 (1976); Brecht v. Abrahamson, 507 U. S. 619 (1993). On the other hand, errors that undermine confidence in the fundamental fairness of the state adjudication certainly justify the issuance of the federal writ. See, e. g., Teague v. Lane, 489 U. S. 288, 311-314 (1989) (quoting Mackey v. United States, 401 U. S. 667, 692-694 (1971) (Harlan, J., concurring in judgments in part and dissenting in part), and quoting Rose v. Lundy, 455 U. S. 509, 544 (1982) (Stevens, J., dissenting)). The deprivation of the right to the effective assistance of counsel recognized in Strickland is such an error. Strickland, 466 U. S., at 686, 697-698.

The warden here contends that federal habeas corpus relief is prohibited by the amendment to 28 U. S. C. § 2254 (1994 ed., Supp. Ill), enacted as a part of the Antiterrorism and Effective Death Penalty Act of 1996 (AEDPA). The relevant portion of that amendment provides:

*376“(d) An application for a writ of habeas corpus on behalf of a person in custody pursuant to the judgment of a State court shall not be granted with respect to any claim that was adjudicated on the merits in State court proceedings unless the adjudication of the claim—

“(1) resulted in a decision that was contrary to, or involved an unreasonable application of, clearly established Federal law, as determined by the Supreme Court of the United States ... .”

In this case, the Court of Appeals applied the construction of the amendment that it had adopted in its earlier opinion in Green v. French, 143 F. 3d 865 (CA4 1998). It read the amendment as prohibiting federal courts from issuing the writ unless:

“(a) the state court decision is in ‘square conflict’ with Supreme Court precedent that is controlling as to law and fact or (b) if no such controlling decision exists, ‘the state court’s resolution of a question of pure law rests upon an objectively unreasonable derivation of legal principles from the relevant [Sjupreme [Cjourt precedents, or if its decision rests upon an objectively unreasonable application. of established principles to new facts,’” 163 F. 3d, at 865 (quoting Green, 143 F. 3d, at 870).

Accordingly, it held that a federal court may issue habeas relief only if “ ‘the state courts have decided the question by interpreting or applying the relevant precedent in a manner that reasonable jurists would all agree is unreasonable,’ ” 163 F. 3d, at.8658

*377We are convinced that that interpretation of the amendment is incorrect. It would impose a test for determining when a legal rule is clearly established that simply cannot be squared with the real practice of decisional law.9 It would apply a standard for determining the “reasonableness” of state-court decisions that is not contained in the statute itself, and that Congress surely did not intend. And it would wrongly require the federal courts, including this Court, to defer to state judges’ interpretations of federal law.

As the Fourth Circuit would have it, a state-court judgment is “unreasonable” in the face of federal law only if all reasonable jurists would agree that the state court was unreasonable. Thus, in this case, for example, even if the Virginia Supreme Court misread our opinion in Lockhart, we could not grant relief unless we believed that none of the judges who agreed with the state court’s interpretation of that ease was a “reasonable jurist.” But the statute says *378nothing about “reasonable judges,” presumably because all, or virtually all, such judges occasionally commit error; they make decisions that in retrospect may be characterized as “unreasonable.” Indeed, it is most unlikely that Congress would deliberately impose such a requirement of unanimity on federal judges. As Congress is acutely aware, reasonable lawyers and lawgivers regularly disagree with one another. Congress surely did not intend that the views of one such judge who might think that relief is not warranted in a particular case should always have greater weight than the contrary, considered judgment of several other reasonable judges.

The inquiry mandated by the amendment relates to the way in which a federal habeas court exercises its duty to decide constitutional questions; the amendment does not alter the underlying grant of jurisdiction in § 2254(a), see n. 7, supra.10 When federal judges exercise their federal-question jurisdiction under the “judicial Power” of Article III of the Constitution, it is “emphatically the province and duty” of those judges to “say what the law is.” Marbury v. Madison, 1 Cranch 137, 177 (1803). At the core of this *379power is the federal courts’ independent responsibility — independent from its coequal branches in the Federal Government, and independent from the separate authority of the several States — to interpret federal law. A construction of AEDPA that would require the federal courts to cede this authority to the courts of the States would be inconsistent with the practice that federal judges have traditionally followed in discharging their duties under Article III of the Constitution. If Congress had intended to require such an important change in the exercise of our jurisdiction, we believe it would have spoken with much greater clarity than is found in the text of AEDPA.

This basic premise informs our interpretation of both parts of § 2254(d)(1): first, the requirement that the determinations of state courts be tested only against “clearly established Federal law, as determined by the Supreme Court of the United States,” and second, the prohibition, on the issuance of the writ unless the state court’s decision is “contrary to, or involved an unreasonable application of,” that clearly established law. We address each part in turn.

The “clearly established law” requirement

In Teague v. Lane, 489 U. S. 288 (1989), we held that the petitioner was not entitled to federal habeas relief because he was relying on a rule of federal law that had not been announced until after his state conviction became final. The antiretroactivity rule recognized in Teague, which prohibits reliance on “new rules,” is the functional equivalent of a statutory provision commanding exclusive reliance on “clearly established law.” Because there is no reason to believe that Congress intended to require federal courts to ask both whether a rule sought on habeas is “new” under Teague— which remains the law — and also whether it is “clearly established” under AEDPA, it seems safe to assume that Congress *380had congruent concepts in mind.11 It is perfectly clear that AEDPA codifies Teague to the extent that Teague requires federal habeas courts to deny relief that is contingent upon a rule of law not clearly established at the time the state conviction became final.12

Teague’s core principles are therefore relevant to our construction of this requirement. Justice Harlan recognized *381the “inevitable difficulties” that come with “attempting ‘to determine whether a particular decision has really announced a “new” rule at all or whether it has simply applied a well-established constitutional principle to govern a ease which is closely analogous to those which have been previously considered in the prior case law.’” Mackey, 401 U. S., at 695 (quoting Desist v. United States, 394 U. S. 244, 263 (1969)). But Teague established some guidance for making this determination, explaining that a federal habeas court operates within the bounds of comity and finality if it applies a rule “dictated by precedent existing at the time the defendant’s conviction became final.” 489 U. S., at 301 (emphasis deleted). A rule that “breaks new ground or imposes a new obligation on the States or the Federal Government,” ibid., falls outside this universe of federal law

To this, AEDPA has added, immediately following the “clearly established law” requirement, a clause limiting the area of relevant law to that “determined by the Supreme Court of the United States.” 28 U. S. C. § 2254(d)(1) (1994 ed., Supp. III). If this Court has not broken sufficient legal ground to establish an asked-for constitutional principle, the lower federal courts cannot themselves establish such a principle with clarity sufficient to satisfy the AEDPA bar. In this respect, we agree with the Seventh Circuit that this clause “extends the principle of Teague by limiting the source of doctrine on which a federal court may rely in addressing the application for a writ.” Lindh v. Murphy, 96 F. 3d 856, 869 (1996). As that court explained:

“This is a retrenchment from former practice, which allowed the United States courts of appeals to rely on their own jurisprudence in addition to that of the Supreme Court. The novelty in this portion of § 2254(d)(1) is not the ‘contrary to’ part but the reference to ‘Federal law, as determined by the Supreme Court of the United States’ (emphasis added). This extends the principle of Teague [v. Lane, 489 U. S. 288 (1989),] by limiting the *382source of doctrine on which a federal court may rely in addressing the application for a writ. It does not, however, purport to limit the federal courts’ independent interpretive authority with respect to federal questions.” Ibid.

A rule that fails to satisfy the foregoing criteria is barred by Teague from application on collateral review, and, similarly, is not available as a basis for relief in a habeas case to which AEDPA applies.

In the context of this case, we also note that, as our precedent interpreting Teague has demonstrated, rules of law may be sufficiently clear for habeas purposes even when they are expressed in terms of a generalized standard rather than- as a bright-line rule. As Justice Kennedy has explained:

“If the rule in question is one which of necessity requires a case-by-case examination of the evidence, then we can tolerate a number of specific applications without saying that those applications themselves create a new rule. . . . Where the beginning point is a rule of this general application, a rule designed for the specific purpose of evaluating a myriad of factual contexts, it will be the infrequent case that yields a result so novel that it forges a new rule, one not dictated by precedent.” Wright v. West, 505 U. S. 277, 308-309 (1992) (opinion concurring in judgment).

Moreover, the determination whether or not a rule is clearly established at the time a state court renders its final judgment of conviction is a question as to which the “federal courts must make an independent evaluation.” Id., at 305 (O’Connor, J., concurring in judgment); accord, id:, at 307 (Kennedy, J., concurring in judgment).

It has been urged, in contrast, that we should read Teague and its progeny to encompass a broader principle of deference requiring federal courts to “validate] ‘reasonable, good-faith interpretations’ of the law” by' state courts. *383Brief for California et al. as Amici Curiae 6 (quoting Butler v. McKellar, 494 U. S. 407, 414 (1990)). The position has been bolstered with references to our statements elucidating the “new rule” inquiry as one turning on whether “reasonable jurists” would agree the rule was not clearly established. Sawyer v. Smith, 497 U. S. 227, 234 (1990). This presumption of deference was in essence the position taken by three Members of this Court in Wright, 505 U. S., at 290-291 (opinion of Thomas, J.) (“[A] federal habeas court 'must defer to the state court’s decision rejecting the claim unless that decision is patently unreasonable’ ”) (quoting Butler, 494 U. S., at 422 (Brennan, J., dissenting)).

Teague, however, does not extend this far. The often repeated language that Teague endorses “reasonable, good-faith interpretations” by state courts is an explanation of policy, not a statement of law. The Teague cases reflect this Court’s view that habeas corpus is not to be used as a second criminal trial, and federal courts are not to run roughshod over the considered findings and judgments of the state courts that conducted the original trial and heard the initial appeals. On the contrary, we have long insisted that federal habeas courts attend closely to those considered decisions, and give them full effect when their findings and judgments are consistent with federal law. See Thompson v. Keohane, 516 U. S. 99, 107-116 (1995). But as Justice O’Connor explained in Wright:

“[T]he duty of the federal court in evaluating whether a rule is 'new’ is not the same as deference;. . . Teague does not direct federal courts to spend less time or effort scrutinizing the existing federal law, on the ground that they can assume the state courts interpreted it properly... .

“[T]he maxim that federal courts should ‘give great weight to the considered conclusions of a coequal state judiciary’ . . . does not mean that we have held in the past that federal courts must presume the correctness *384of a state court’s legal conclusions on habeas, or that a state court’s incorrect legal determination has ever been allowed to stand because it was reasonable. We have always held that federal courts, even on habeas, have an independent obligation to say what the law is.” 505 U. S., at 305 (opinion concurring in judgment).

We are convinced that in the phrase, “clearly established law,” Congress did not intend to modify that independent obligation.

The “contrary to, or an unreasonable application of” requirement

The message that Congress intended to convey by using the phrases “contrary to” and “unreasonable application of” is not entirely clear. The prevailing view in the Circuits is that the former phrase requires de novo review of “pure” questions of law and the latter requires some sort of “reason-ability” review of so-called mixed questions of law and fact. See, e. g., Neelley v. Nagle, 138 F. 3d 917 (CA11 1998); Drinkard v. Johnson, 97 F. 3d 751 (CA5 1996); Lindh v. Murphy, 96 F. 3d 856 (CA7 1996) (en banc), rev’d on other grounds, 521 U. S. 320 (1997).

We are not persuaded that the phrases define two mutually exclusive categories of questions. Most constitutional questions that arise in habeas corpus proceedings — and therefore most “decisions” to be made — require the federal judge to apply a rule of law to a set of facts, some of which may be disputed and some undisputed. For example, an erroneous conclusion that particular circumstances established the voluntariness of a confession, or that there exists a conflict of interest when one attorney represents multiple defendants, may well be described either as “contrary to” or as an “unreasonable application of” the governing rule of law. Cf. Miller v. Fenton, 474 U. S. 104, 116 (1985); Cuyler v. Sullivan, 446 U. S. 335, 341-342 (1980). In constitutional adjudication, as in the common law, rules of law often develop *385incrementally as earlier decisions are applied to new factual situations. See Wright, 505 U. S., at 307 (Kennedy, J., concurring in judgment). But rules that depend upon such . elaboration are hardly less lawlike than those that establish a bright-line test.

Indeed, our pre-AEDPA efforts to distinguish questions of fact, questions of law, and “mixed questions,” and to create an appropriate standard of habeas review for each, generated some not insubstantial differences of opinion as to which issues of law fell into which category of question, and as to which standard of review applied to each. See Thompson, 516 U. S., at 110-111 (acknowledging “'that the Court has not charted an entirely clear course in this area’ ” and that “the proper characterization of a question as one of fact or law is sometimes slippery”) (quoting Miller, 474 U. S., at 113). We thus think the Fourth Circuit was correct when it attributed the lack of clarity in the statute, in part, to the overlapping meanings of the phrases “contrary to” and “unreasonable application of.” See Green, 143 F. 3d, at 870.

The statutory text likewise does not obviously prescribe a specific, recognizable standard of review for dealing with either phrase. Significantly, it does not use any term, such as “de novo” or “plain error,” that would easily identify a familiar standard of review. Rather, the text is fairly read simply as a command that a federal court not issue the ha-beas writ unless the state court was wrong as a matter of law or unreasonable in its application of law in a given case. The suggestion that a wrong state-court “decision” — a legal judgment rendered “after consideration of facts, and . . . law,” Black’s Law Dictionary 407 (6th ed. 1990) (emphasis added) — may no longer be redressed through habeas (because it is unreachable under the “unreasonable application” phrase) is based on a mistaken insistence that the § 2254(d)(1) phrases have not only independent, but mutually exclusive, meanings. Whether or not a federal court can issue the writ “under [the] 'unreasonable application’ clause,” the statute is *386clear that habeas may issue under § 2254(d)(1) if a state-court “decision” is “contrary to . . . clearly established Federal law.” We thus anticipate that there will be a variety of cases, like this one, in which both phrases may be implicated.

Even though we cannot conclude that the phrases establish “a body of rigid rules,” they do express a “mood” that the Federal Judiciary must respect. Universal Camera Corp. v. NLRB, 340 U. S. 474, 487 (1951). In this respect, it seems clear that Congress intended federal judges to attend with the utmost care to state-court decisions, including all of the reasons supporting their decisions, before concluding that those proceedings were infected by constitutional error sufficiently serious to warrant the issuance of the writ. Likewise, the statute in a separate provision provides for the habeas remedy when a state-court decision “was based on an unreasonable determination of the facts in light of the evidence presented in the State court proceeding.” 28 U. S. C. § 2254(d)(2) (1994 ed., Supp. Ill) (emphasis added). While this provision is not before us in this case, it provides relevant context for our interpretation of § 2254(d)(1); in this respect,-it bolsters our conviction that federal habeas courts must make as the starting point of their analysis the state courts’ determinations of fact, including that aspect of a “mixed question” that rests on a finding of fact. AEDPA plainly sought to ensure a level of “deference to the determinations of state courts,” provided those determinations did not conflict with federal law or apply federal law in an unreasonable way. H. R. Conf. Rep. No. 104-518, p. Ill (1996). Congress wished to curb delays, to prevent “retrials” on federal habeas, and to give effect to state convictions to the extent possible under law. When federal courts are able to fulfill these goals within the bounds of the law, AEDPA instructs them to do so.

On the other hand, it is significant that the word “deference” does not appear in the text of the statute itself. Neither the legislative history nor the statutory text suggests *387any difference in the so-called “deference” depending on which of the two phrases is implicated.13 Whatever “deference” Congress had in mind with respect to both phrases, it surely is not a requirement that federal courts actually defer to a state-court application of the federal law that is, in the independent judgment of the federal court, in error. As Judge Easterbrook noted with respect to the phrase “contrary to”:

“Section 2254(d) requires us to give state courts’ opinions a respectful reading, and to listen carefully to their conclusions, but when the state court addresses a legal question, it is the law 'as determined by the Supreme Court of the United States’ that prevails.” Lindh, 96 F. 3d, at 869.14

*388Our disagreement with the Court about the precise meaning of the phrase “contrary to,” and the word “unreasonable,” is, of course, important, but should affect only a narrow category of cases. The simplest and first definition of “contrary to” as a phrase is “in conflict with.” Webster’s *389Ninth New Collegiate Dictionary 285 (1983). In this sense, we think the phrase surely capacious enough to include a finding that the state-court “decision” is simply “erroneous” or wrong. (We hasten to add that even “diametrically different” from, or “opposite” to, an established federal law would seem to include “decisions” that are wrong in light of that law.) And there is nothing in the phrase “contrary to” — as the Court appears to agree — that implies anything less than independent review by the federal courts. Moreover, state-court decisions that do not “conflict” with federal law will rarely be “unreasonable” under either the Court’s reading of the statute or ours. We all agree that state-court judgments must be upheld unless, after the closest examination of the state-court judgment, a federal court is firmly convinced that a federal constitutional right has been violated. Our difference is as to the cases in which, at first blush, a state-court judgment seems entirely reasonable, but thorough analysis by a federal court produces a firm conviction that that judgment is infected by constitutional error. In our view, such an erroneous judgment is “unreasonable” within the meaning of the Act even though that conclusion was not immediately apparent.

In sum, the statute directs federal courts to attend to every state-court judgment with utmost care, but it does not require them to defer to the opinion of every reasonable state-court judge on the content of federal law. If, after carefully weighing all the reasons for accepting a state court’s judgment, a federal court is convinced that a prisoner’s custody — or, as in this case, his sentence of death — violates the Constitution, that independent judgment should prevail. Otherwise the federal “law as determined by the Supreme Court of the United States” might be applied by the federal courts one way in Virginia and another way in California. In light of the well-recognized interest in ensuring that federal courts interpret federal law in a uniform *390way,15 we are convinced that Congress did not intend the statute to produce such a result.

III

In this ease, Williams contends that he was denied his constitutionally guaranteed right to the effective assistance of counsel when his trial lawyers failed , to investigate and to present substantial mitigating evidence to the sentencing jury. The threshold question under AEDPA is whether Williams seeks to apply a rule of law that was clearly established at the time his state-court conviction became final. That question is easily answered because the merits of his claim are squarely governed by our holding in Strickland v. Washington, 466 U. S. 668 (1984).

We explained in Strickland that a violation of the right on which Williams relies has two components:

“First, the defendant must show that counsel’s performance was deficient. This requires showing that counsel made errors so serious that counsel was not functioning as the ‘counsel’ guaranteed the defendant by the Sixth Amendment. Second, the defendant must show that the deficient performance prejudiced the defense. This requires showing that counsel’s errors were so serious as to deprive the defendant of a fair trial, a trial whose result is reliable.” Id., at 687.

To establish ineffectiveness, a “defendant must show that counsel’s representation fell below an objective standard of *391reasonableness.” Id., at 688. To establish prejudice he “must show that there is a reasonable probability that, but for counsel’s unprofessional errors, the result of the proceeding would have been different. A reasonable probability is a probability sufficient to undermine confidence in the outcome.” Id., at 694.

It is past question that the rule set forth in Strickland qualifies as “clearly established Federal law, as determined by the Supreme Court of the United States.” That the Strickland test “of necessity requires a case-by-ease examination of the evidence,” Wright, 505 U. S., at 308 (Kennedy, J., concurring in judgment), obviates neither the clarity of the rule nor the extent to which the rule must be seen as “established” by this Court. This Court’s precedent “dictated” that the Virginia Supreme Court apply the Strickland test at the time that court entertained Williams’ ineffective-assistance claim. Teague, 489 U. S., at 301. And it can hardly be said that recognizing the right to effective counsel “breaks new ground or imposes a new obligation on the States,” ibid. Williams is therefore entitled to relief if the Virginia Supreme Court’s decision rejecting his ineffective-assistance claim was either “contrary to, or involved an unreasonable application of,” that established law. It was both.

IV

The Virginia Supreme Court erred in holding that our decision in Lockhart v. Fretwell, 506 U. S. 364 (1993), modified or in some way supplanted the rule set down in Strickland. It is true that while the Strickland test provides sufficient guidance for resolving virtually all ineffective-assistance-of-counsel claims, there are situations in which the overriding focus on fundamental fairness may affect the analysis. Thus, on the one hand, as Strickland itself explained, there are a few situations in which prejudice may be presumed. 466 U. S., at 692. And, on the other hand, there are also situations in which it would be unjust to characterize the *392likelihood of a different outcome as legitimate “prejudice.” Even if a defendant’s false testimony might have persuaded the jury to acquit him, it is not fundamentally unfair to conclude that he was not prejudiced by counsel’s interference with his intended perjury. Nix v. Whiteside, 475 U. S. 157, 175-176 (1986).

Similarly, in Lockhart, we concluded that, given the overriding interest in fundamental fairness, the likelihood of a different outcome attributable to an incorrect interpretation of the law should be regarded as a potential “windfall” to the defendant rather than the legitimate “prejudice” contemplated by our opinion in Strickland. The death sentence that Arkansas had imposed on Bobby Ray Fretwell was based on an aggravating circumstance (murder committed for pecuniary gain) that duplicated an element of the underlying felony (murder in the course of a robbery). Shortly before the trial, the United States Court of Appeals for the Eighth Circuit had held that such “double counting” was impermissible, see Collins v. Lockhart, 754 F. 2d 258, 265 (1985), but Fretwell’s lawyer (presumably because he was unaware of the Collins decision) failed-to object to the use of the pecuniary gain aggravator. Before Fretwell’s claim for federal habeas corpus relief reached this Court, the Collins ease was overruled.16 Accordingly, even though the Arkansas trial judge probably would have sustained a timely objection to the double counting, it had become clear that the State had a right to rely on the disputed aggravating circumstance. Because the ineffectiveness of Fretwell’s counsel had not deprived him of any substantive or procedural right to which the law entitled him, we held that his *393claim did not satisfy the “prejudice” component of the Strickland test.17

Cases such as Nix v. Whiteside, 475 U. S. 157 (1986), and Lockhart v. Fretwell, 506 U. S. 364 (1993), do not justify a departure from a straightforward application of Strickland when the ineffectiveness of counsel does deprive the defendant of a substantive or procedural right to which the law entitles him.18 In the instant ease, it is undisputed that Williams had a right — indeed, a constitutionally protected right — to provide the jury with the mitigating evidence that his trial counsel either failed to discover or failed to offer.

Nevertheless, the Virginia Supreme Court read our decision in Lockhart to require a separate inquiry into fundamental fairness even when Williams is able to show that his lawyer was ineffective and that his ineffectiveness probably affected the outcome of the proceeding. It wrote:

*394“ The prisoner argues there 'is a “reasonable probability” that at least one juror would have been moved to spare Petitioner’s life had he heard’ the mitigation evidence developed at the habeas hearing that was not presented at the trial. Summarizing, he contends there 'is a “reasonable probability” that had at least one juror heard any of this evidence — let alone all of this evidence — the outcome of this case would have been different.’

“We reject these contentions. The prisoner’s discussion flies in the face of the Supreme Court’s admonition in Lockhart, supra, that 'an analysis focusing solely on mere outcome determination, without attention to whether the result of the proceeding was fundamentally unfair or unreliable, is defective.’ ” 254 Va., at 25, 487 S. E. 2d, at 199.

Unlike the Virginia Supreme Court, the state trial judge omitted any reference to Lockhart and simply relied on our opinion in Strickland as stating the correct standard for judging ineffective-assistance claims. With respect to the prejudice component, he wrote:

“Even if a Petitioner shows that counsel’s performance was deficient, however, he must also show prejudice. Petitioner must show 'that there is a reasonable probability that but for counsel’s unprofessional errors, the result. . . would have been different.’ Strickland, 466 U. S. at 694. ‘A reasonable probability is a probability sufficient to undermine confidence in the outcome.’ Id. Indeed, it is insufficient to show only that the errors had some conceivable effect on the outcome of the proceeding, because virtually every act or omission of counsel would meet that test. Id. at 693. The petitioner bears the 'highly demanding’ and ‘heavy burden’ in establishing actual prejudice.” App. 417.

*395The trial judge analyzed the ineffective-assistance claim under the correct standard; the Virginia Supreme Court did not.

We are likewise persuaded that the Virginia trial judge correctly applied both components of that standard to Williams’ ineffectiveness claim. Although he concluded that counsel competently handled the guilt phase of the trial, he found that their representation during the sentencing phase fell short of professional standards — a judgment barely disputed by the State in its brief to this Court. The record establishes that counsel did not begin to prepare for that phase of the proceeding until a week before the trial. Id., at 207, 227. They failed to conduct an investigation that would have uncovered extensive records graphically describing Williams’ nightmarish childhood, not because of any strategic calculation but because they incorrectly thought that state law barred access to such records. Had they done so, the jury would have learned that Williams’ parents had been imprisoned for the criminal neglect of Williams and his siblings,19 that Williams had been severely and repeatedly beaten by his father, that he had been committed to the custody of the social services bureau for two years during his parents’ incarceration (including one stint in an abusive foster home), and then, after his parents were released from prison, had been returned to his parents’ custody.

*396Counsel failed to introduce available evidence that Williams was “borderline mentally retarded” and did not advance beyond sixth grade in school. Id., at 595. They failed to seek prison records recording Williams’ commendations for helping to crack a prison drug ring and for returning a guard’s missing wallet, or the testimony of prison officials who described Williams as among the inmates “least likely to act in a violent, dangerous or provocative way.” Id., at 569,588. Counsel failed even to return the phone call of a certified public accountant who had offered to testify that he had visited Williams frequently when Williams was incarcerated as part of a prison ministry program, that Williams “seemed to thrive in a more regimented and structured environment,” and that Williams was proud of the carpentry degree he earned while in prison. Id., at 568-566.

Of course, not all of the additional evidence was favorable to Williams. The juvenile records revealed that he had been thrice committed to the juvenile system — for aiding and abetting larceny when he was 11 years old, for pulling a false fire alarm when he was 12, and for breaking and entering when he was 15. Id., at 584-536. But as the Federal District Court correctly observed, the failure to introduce the comparatively voluminous amount of evidence that did speak in Williams’ favor was not justified by a tactical decision to focus on Williams’ voluntary confession. Whether or not those omissions were sufficiently prejudicial to have affected the outcome of sentencing, they clearly demonstrate that trial counsel did not fulfill their oblígátion to conduct a thorough investigation of the defendant’s background. See 1 ABA Standards for Criminal Justice 4-4.1, commentary, p. 4-55 (2d ed. 1980).

We are also persuaded, unlike the Virginia Supreme Court, that counsel’s unprofessional service prejudiced Williams within the meaning of Strickland. After hearing the additional evidence developed in the postconviction proceedings, the very judge who presided at Williams’ trial, and who once *397determined that the death penalty was “just” and “appropriate,” concluded that there existed “a reasonable probability that the result of the sentencing phase would have been different” if the jury had heard that evidence. App. 429. We do not agree with the Virginia Supreme Court that Judge Ingram’s conclusion should be discounted because he apparently adopted “a per se approach to the prejudice element” that placed undue “emphasis on mere outcome determination.” 254 Va., at 26-27, 487 S.E. 2d, at 200. Judge Ingram did stress the importance of mitigation evidence in making his “outcome determination,” but it is clear that his predictive judgment rested on his assessment of the totality of the omitted evidence rather than on the notion that a single item of omitted evidence, no matter how trivial, would require a new hearing.

The Virginia Supreme Court’s own analysis of prejudice reaching the contrary conclusion was thus unreasonable in at least two respects.. First, as we have already explained, the State Supreme Court mischaracterized at best the appropriate rule, made clear by this Court in Strickland, for determining whether counsel’s assistance was effective within the meaning of the Constitution. While it may also have conducted an “outcome determinative” analysis of its own, 254 Va., at 27, 487 S. E. 2d, at 200, it is evident to us that the court’s decision turned on its erroneous view that a “mere” difference in outcome is not sufficient to establish constitutionally ineffective assistance of counsel. See supra, at 394. Its analysis in this respect was thus not only “contrary to,” but also, inasmuch as the Virginia Supreme Court relied on the inapplicable exception recognized in Lockhart, an “unreasonable application of” the clear law as established by this Court.

Second, the State Supreme Court’s prejudice determination was unreasonable insofar as it failed to evaluate the totality of the available mitigation evidence — both that adduced at trial, and the evidence adduced in the habeas pro*398ceeding — in reweighing it against the evidence in aggravation. See Clemons v. Mississippi, 494 U. S. 738, 751-752 (1990). This error is apparent in its consideration of the additional mitigation evidence developed in the postconviction proceedings. The court correctly found that as to “the factual part of the mixed question,” there was “really . . . n[o] . . . dispute” that available mitigation evidence was not presented at trial. 254 Va., at 24, 487 S. E. 2d, at 198. As to the prejudice determination comprising the “legal part” of its analysis, id., at 23-25, 487 S. E. 2d, at 198-199, it correctly emphasized the strength of the prosecution evidence supporting the future dangerousness aggravating circumstance.

But the state court failed even to mention the sole argument in mitigation that trial counsel did advance — Williams turned himself in, alerting police to a crime they otherwise would never have discovered, expressing remorse for his actions, and cooperating with the police after that. While this, coupled with the prison records and guard testimony, may not have overcome a finding of future dangerousness, the graphic description of Williams’ childhood, filled with abuse and privation, or the reality that he was “borderline mentally retarded,” might well have influenced the jury’s appraisal of his moral culpability. See Boyde v. California, 494 U. S. 370, 387 (1990). The circumstances recited in his several confessions are consistent with the view that in each case his violent behavior was a compulsive reaction rather than the product of cold-blooded premeditation. Mitigating evidence unrelated to dangerousness may alter the jury’s selection of penalty, even if it does not undermine or rebut the prosecution’s death-eligibility case. The Virginia Supreme Court did not entertain that possibility. It thus failed to accord appropriate weight to the body of mitigation evidence available to trial counsel.

V

In our judgment, the state trial judge was correct both in his recognition of the established legal standard for deter-*399milling counsel's effectiveness, and in his conclusion that the entire postconviction record, viewed as a whole and cumulative of mitigation evidence presented originally, raised “a reasonable probability that the result of the sentencing proceeding would have been different” if competent counsel had presented and explained the significance of all the available evidence. It follows that the Virginia Supreme Court rendered a “decision that was contrary to, or involved an unreasonable application of, clearly established Federal law.” Williams’ constitutional right to the effective assistance of counsel as defined in Strickland v. Washington, 466 U. S. 668 (1984), was violated.

Accordingly, the judgment of the Court of Appeals is reversed, and the case is remanded for further proceedings.

It is so ordered.

delivered the opinion of the Court with respect to Part II (except as to the footnote), concurred in part, and concurred in the judgment.*

In 1996, Congress enacted tlm Antiterrorism and Effective Death Penalty Act (AEDPA). In that Act, Congress placed a new restriction on the power of federal courts to grant writs of habeas corpus to state prisoners. The relevant provision, 28 U. S. C. § 2254(d)(1) (1994 ed., Supp. Ill), prohibits a federal court from granting an application for a writ of habeas corpus with respect to a claim adjudicated on the merits in state court unless that adjudication “resulted in a decision that was contrary to, or involved an unreasonable application of, clearly established Federal law, as determined by the Supreme Court of the United States.” The Court holds today that the Virginia Supreme Court’s adjudication *400of Terry Williams’ application for state habeas corpus relief resulted in just such a decision, I agree with that determination and join Parts I, III, and IV of the Court’s opinion. Because I disagree, however, with the interpretation of § 2254(d)(1) set forth in Part II of Justice Stevens’ opinion, I write separately to explain my views.

I

Before 1996, this Court held that a federal court entertaining a state prisoner’s application for habeas relief must exercise its independent judgment when deciding both questions of constitutional law and mixed constitutional questions (i. e., application of constitutional law to fact). See, e. g., Miller v. Fenton, 474 U. S. 104, 112 (1985). In other words, a federal habeas court owed no deference to a state court’s resolution of such questions of law or mixed questions. In 1991, in the case of Wright v. West, 502 U. S. 1021, we revisited our prior holdings by asking the parties to address the following question in their briefs:

“In determining whether to grant a petition for writ of habeas corpus by a person in custody pursuant to the judgment of a state court, should a federal court give deference to the state court’s application of law to the specific facts of the petitioner’s case or should it review the state court’s determination de novo?” Ibid.

Although our ultimate decision did not turn on the answer to that question, our several opinions did join issue on it. See Wright v. West, 505 U. S. 277 (1992).

Justice Thomas, announcing the judgment of the Court, acknowledged that our precedents had “treat[ed] as settled the rule that mixed constitutional questions are ‘subject to plenary federal review’ on habeas.” Id., at 289 (quoting Miller, supra, at 112). He contended, nevertheless, that those decisions did not foreclose the Court from applying a rule of deferential review for reasonableness in future cases. *401See 505 U. S., at 287-290. According to Justice Thomas, the reliance of our precedents on Brown v. Allen, 344 U. S. 443 (1953), was erroneous because the Court in Brown never explored in detail whether a federal habeas court, to deny a state prisoner’s application, must conclude that the relevant state-court adjudication was "correct” or merely that it was “reasonable.” Wright, supra, at 287. Justice Thomas suggested that the time to revisit our decisions may have been at hand, given that our more recent habeas jurisprudence in the nonretroaetivity context, see, e.g., Teague v. Lane, 489 U. S. 288 (1989), had called into question the then-settled rule of independent review of mixed constitutional questions. Wright, 505 U. S., at 291-292, 294.

I wrote separately in Wright because I believed Justice Thomas had “understate[dj the certainty with which Brown v. Allen rejected a deferential standard of review of issues of law.” Id., at 300. I also explained that we had considered the standard of review applicable to mixed constitutional questions on numerous occasions and each time we concluded that federal habeas courts had a duty to evaluate such questions independently. Id., at 301-303. With respect to Justice Thomas’ suggestion that Teague and its progeny called into question the vitality of the independent-review rule, I noted that “Teague did not establish a ‘deferential’ standard of review” because “[i]t did not establish a standard of review at all.” 505 U. S., at 303-304. While Teague did hold that state prisoners could not receive “the retroactive benefit of new rules of law,” it “did not create any deferential standard of review with regard to old rules.” 505 U. S., at 304 (emphasis in original).

Finally, and perhaps most importantly for purposes of today’s ease, I stated my disagreement with Justice Thomas’ suggestion that de novo review is incompatible with the maxim that federal habeas courts should “give great weight to the considered conclusions of a coequal state judiciary,” Miller, supra, at 112. Our statement in Miller signified *402only that a state-court decision is due the same respect as any other “persuasive, well-reasoned authority.” Wright, 505 U. S., at 305. “But this does not mean that we have held in the past that federal courts must presume the correctness of a state court’s legal conclusions on habeas, or that a state court’s incorrect legal determination has ever been allowed to stand because it was reasonable. We have always held that federal courts, even on habeas, have an independent obligation to say what the law is.” Ibid. Under the federal habeas statute as it stood in 1992, then, our precedents dictated that a federal court should grant a state prisoner’s petition for habeas relief if that court were to conclude in its independent judgment that the relevant state court had erred on a question of constitutional law or on a mixed constitutional question.

If today’s case were governed by the federal habeas statute prior to Congress’ enactment of AEDPA in 1996,1 would agree with Justice Stevens that Williams’ petition for ha-beas relief must be granted if we, in our independent judgment, were to conclude that his Sixth Amendment right to effective assistance of counsel was violated. See ante, at 389.

H

A

Williams’ case is not governed by the pre-1996 version of the habeas statute. Because he filed his petition in December 1997, Williams’ case is governed by the statute as amended by AEDPA. Section 2254 now provides:

“(d) An application for a writ of habeas corpus on behalf of a person in custody pursuant to the judgment of a State court shall not be granted with respect to any claim that was adjudicated on the merits in State court proceedings unless the adjudication of the claim—

“(1) resulted in a decision that was contrary to, or involved an unreasonable application of, clearly estab-*403fished Federal law, as determined by the Supreme Court of the United States.”

Accordingly, for Williams to obtain federal habeas relief, he must first demonstrate that his case satisfies the condition set by § 2254(d)(1). That provision modifies the role of federal habeas courts in reviewing petitions filed by state prisoners.

Justice Stevens’ opinion in Part II essentially contends that § 2254(d)(1) does not alter the previously settled rule of independent review. Indeed, the opinion concludes its statutory inquiry with the somewhat empty finding that §2254(d)(1) does no more than express a “‘mood’ that the Federal Judiciary must respect.” Ante, at 386. For Justice Stevens, the congressionally enacted “mood” has two important qualities. First, “federal courts [must] attend to every state-court judgment with utmost care” by “carefully weighing all the reasons for accepting a state court’s judgment.” Ante, at 389. Second, if a federal court undertakes that careful review and yet remains convinced that a prisoner’s custody violates the Constitution, “that independent judgment should prevail.” Ibid.

One need look no further than our decision in Miller to see that Justice Stevens’ interpretation of § 2254(d)(1) gives the 1996 amendment no effect whatsoever. The command that federal courts should now use the “utmost care” by “carefully weighing” the reasons supporting a state court’s judgment echoes our pre-AEDPA statement in Miller that federal habeas courts “should, of course, give great weight to the considered conclusions of a coequal state judiciary.” 474 U. S., at 112. Similarly, the requirement that the independent judgment of a federal court must in the end prevail essentially repeats the conclusion we reached in the very next sentence in Miller with respect to the specific issue presented there: “But, as we now reaffirm, the ultimate question whether, under the totality of the circumstances, the challenged confession was obtained in a manner compat*404ible with the requirements of the Constitution is a matter for independent federal determination.” Ibid, (emphasis added).

That Justice Stevens would find the new § 2254(d)(1) to have no effect on the prior law of habeas corpus is remarkable given his apparent acknowledgment that Congress wished to bring change to the field. See ante, at 386 (“Congress wished to curb delays, to prevent ‘retrials’ on federal habeas, and to give effect to state convictions to the extent possible under law”). That acknowledgment is correct and significant to this case. It cannot be disputed that Congress viewed § 2254(d)(1) as an important means by which its goals for habeas reform would be achieved.

Justice Stevens arrives at his erroneous interpretation by means of one critical misstep. He fails to give independent meaning to both the “contrary to” and “unreasonable application” clauses of the statute. See, e. g., ante, at 384 (“We are not persuaded that the phrases define two mutually exclusive categories of questions”). By reading § 2254(d)(1) as one general restriction on the power of the federal habeas court, Justice Stevens manages to avoid confronting the specific meaning of the statute’s “unreasonable application” clause and its ramifications for the independent-review rule. It is, however, a cardinal principle of statutory construction that we must “ ‘give effect, if possible, to every clause and word of a statute.’ ” United States v. Menasche, 348 U. S. 528, 538-539 (1955) (quoting Montclair v. Ramsdell, 107 U. S. 147, 152 (1883)). Section 2254(d)(1) defines two categories of cases in which a state prisoner may obtain federal habeas relief with respect to a claim adjudicated on the merits in state court. Under the statute, a federal court may grant a writ of habeas corpus if the relevant state-court decision was either (1) “contrary to . . . clearly established Federal law, as determined by the Supreme Court of the United States,” or (2) “involved an unreasonable application of.. . clearly *405established Federal law, as determined by the Supreme Court of the United States.” (Emphases added.)

The Court of Appeals for the Fourth Circuit properly accorded both the “contrary to” and “unreasonable application” clauses independent meaning. The Fourth Circuit’s interpretation of § 2254(d)(1) in Williams’ case relied, in turn, on that court’s previous decision in Green v. French, 143 F. 3d 865 (1998), cert. denied, 525 U. S. 1090 (1999). See 163 F. 3d 860, 866 (CA4 1998) (“[Tjhe standard of review enunciated in Green v. French continues to be the binding law of this Circuit”) . With respect to the first of the two statutory clauses, the Fourth Circuit held in Green that a state-court decision can be “contrary to” this Court’s clearly established precedent in two ways. First, a state-court decision is contrary to this Court’s precedent if the state court arrives at a conclusion opposite to that reached by this Court on a question of law. Second, a state-court decision is also contrary to this Court’s precedent if the state court confronts facts that are materially indistinguishable from a relevant Supreme Court precedent and arrives at a result opposite to ours. See 143 F. 3d, at 869-870.

The word “contrary” is commonly understood to mean “diametrically different,” “opposite in character or nature,” or “mutually opposed.” Webster’s Third New International Dictionary 495 (1976). The text of § 2254(d)(1) therefore suggests that the state court’s decision must be substantially different from the relevant precedent of this Court. The Fourth Circuit’s interpretation of the “contrary to” clause accurately reflects this textual meaning. A state-court decision will certainly be contrary to our clearly established precedent if the state court applies a rule that contradicts the governing law set forth in our cases. Take, for example, our decision in Strickland v. Washington, 466 U. S. 668 (1984). If a state court were to reject a prisoner’s claim of ineffective assistance of counsel on the grounds that the *406prisoner had not established by a preponderance of the evidence that the result of his criminal proceeding would have been different, that decision would be “diametrically different,” “opposite in character or nature,” and “mutually opposed” to our clearly established precedent because we held in Strickland that the prisoner need only demonstrate a “reasonable probability that... the result of the proceeding would have been different.” Id., at 694. A state-court decision will also be contrary to this Court’s clearly established precedent if the state court confronts a set of facts that are materially indistinguishable from a decision of this Court and nevertheless arrives at a result different from our precedent. Accordingly, in either of these two scenarios, a federal court will be unconstrained by § 2254(d)(1) because the state-court decision falls within that provision’s “contrary to” clause.

On the other hand, a run-of-the-mill state-court decision applying the correct legal rule from our cases to the facts of a prisoner’s case would not fit comfortably within §2254(d)(l)’s “contrary to” clause. Assume, for example, that a state-court decision on a prisoner’s ineffective-assistance claim correctly identifies Strickland as the controlling legal authority and, applying that framework, rejects the prisoner’s claim. Quite clearly, the state-court decision would be in accord with our decision in Strickland as to the legal prerequisites for establishing an ineffective-assistance claim, even assuming the federal court considering the prisoner’s habeas application might reach a different result applying the Strickland framework itself. It is difficult, however, to describe such a run-of-the-mill state-court decision as “diametrically different” from, “opposite in character or nature” from, or “mutually opposed” to Strickland, our clearly established precedent. Although the state-court decision may be contrary to the federal court’s conception of how Strickland ought to be applied in that particular case, the decision is not “mutually opposed” to Strickland itself.

*407Justice Stevens would instead construe § 2254(d)(l)’s “contrary to” clause to encompass such a routine state-court decision. That construction, however, saps the “unreasonable application” clause of any meaning. If a federal habeas court can, under the “contrary to” clause, issue the writ whenever it concludes that the state court’s application of clearly established federal law was incorrect, the “unreasonable application” clause becomes a nullity. We must, however, if possible, give meaning to every clause of the statute. Justice Stevens not only makes no attempt to do so, but also construes the “contrary to” clause in a manner that ensures that the “unreasonable application” clause will have no independent meaning. See ante, at 385-386, 388-390. We reject that expansive interpretation of the statute. Reading § 2254(d)(l)’s “contrary to” clause to permit a federal court to grant relief in cases where a state court’s error is limited to the manner in which it applies Supreme Court precedent is suspect given the logical and natural fit of the neighboring “unreasonable application” clause to such cases.

The Fourth Circuit’s interpretation of the “unreasonable application” clause of § 2254(d)(1) is generally correct. That court held in Green that a state-court decision can involve an “unreasonable application” of this Court’s clearly established precedent in two ways. First, a state-court decision involves an unreasonable application of this Court’s precedent if the state court identifies the correct governing legal rule from this Court’s cases but unreasonably applies it to the facts of the particular state prisoner’s ease. Second, a state-court decision also involves an unreasonable application of this Court’s precedent if the state court either unreasonably extends a legal principle from our precedent to a new context where it should not apply or unreasonably refuses to extend that principle to a new context where it should apply. See 143 F. 3d, at 869-870.

decision that correctly identifies the governing legal rule but applies it unreasonably to the facts of a *408particular prisoner’s case certainly would qualify as a decision “involv[ing] an unreasonable application of . . . clearly established Federal law.” Indeed, we used the almost identical phrase “application of law” to describe a state court’s application of law to fact in the certiorari question we posed to the parties in Wright*

The Fourth Circuit also held in Green that state-court decisions that unreasonably extend a legal principle from our precedent to a new context where it should not apply (or unreasonably refuse to extend a legal principle to a new context where it should apply) should be analyzed under §2254(d)(l)’s “unreasonable application” clause. See 143 F. 3d, at 869-870. Although that holding may perhaps be correct, the classification does have some problems of precision. Just as it is sometimes difficult to distinguish a mixed question of law and fact from a question of fact, it will often be difficult to identify separately those state-court decisions that involve an unreasonable application of a legal principle (or an unreasonable failure to apply a legal principle) to a new context. Indeed, on the one hand, in some cases it will be hard to distinguish a decision involving an unreasonable extension of a legal principle from a decision involving an unreasonable application of law to facts. On the other hand, in many of the same cases it will also be difficult to distinguish a decision involving an unreasonable extension of a legal principle from a decision that “arrives at a conclusion opposite to that reached by this Court on a question of law,” supra, at 405. Today’s case does not require us to decide how *409such “extension of legal principle” cases should be treated under § 2254(d)(1). For now it is sufficient to hold that when a state-court decision unreasonably applies the law of this Court to the facts of a prisoner’s case, a federal court applying § 2254(d)(1) may conclude that the state-court decision falls within that provision’s “unreasonable application” clause.

B

There remains the task of defining what exactly qualifies as an “unreasonable application” of law under § 2254(d)(1). The Fourth Circuit held in Green that a state-court decision involves an “unreasonable application of . . . clearly established Federal law” only if the state court has applied federal law “in a manner that reasonable jurists would all agree is unreasonable.” 143 F. 3d, at 870. The placement of this additional overlay on the “unreasonable application” clause was erroneous. It is difficult to fault the Fourth Circuit for using this language given the fact that we have employed nearly identical terminology to describe the related inquiry undertaken by federal courts in applying the nonretroactivity rule of Teague. For example, in Lambrix v. Singletary, 520 U. S. 518 (1997), we stated that a new rule is not dictated by precedent unless it would be “apparent to all reasonable jurists.” Id., at 528 (emphasis added). In Graham v. Collins, 506 U. S. 461 (1993), another nonretroactivity case, we employed similar language, stating that we could not say “that all reasonable jurists would have deemed themselves compelled to accept Graham’s claim in 1984.” Id., at 477 (emphasis added).

Defining an “unreasonable application” by reference to a “reasonable jurist,” however, is of little assistance to the courts that must apply § 2254(d)(1) and, in fact, may be misleading. Stated simply, a federal habeas court making the “unreasonable application” inquiry should ask whether the state court’s application of clearly established federal law was objectively unreasonable. The federal habeas court *410should not transform the inquiry into a subjective one by resting its determination instead on the simple fact that at least one of the Nation’s jurists has applied the relevant federal law in the same manner the state court did in the habeas petitioner's case. The “all reasonable jurists” standard would tend to mislead federal habeas courts by focusing their attention on a subjective inquiry rather than on an objective one. For example, the Fifth Circuit appears to have applied its “reasonable jurist” standard in just such a subjective manner. See Drinkard v. Johnson, 97 F. 3d 751, 769 (1996) (holding that state court’s application of federal law was not unreasonable because the Fifth Circuit panel split 2-1 on the underlying mixed constitutional question), cert. denied, 520 U. S. 1107 (1997). As I explained in Wright with respect to the “reasonable jurist” standard in the Teague context, “[e]ven though we have characterized the new rule inquiry as whether ‘reasonable jurists’ could disagree as to whether a result is dictated by precedent, the standard for determining when a case establishes a new rule is ‘objective,’ and the mere existence of conflicting authority does not necessarily mean a rule is new.” 505 U. S., at 304 (citation omitted).

The term “unreasonable” is no doubt difficult to define. That said, it is a common term in the legal world and, accordingly, federal judges are familiar with its meaning. For purposes of today’s opinion, the most important point is that an unreasonable application of federal law is different from an incorrect application of federal law. Our opinions in Wright, for example, make that difference clear. Justice Thomas’ criticism of this Court’s subsequent reliance on Brown turned on that distinction. The Court in Brown, Justice Thomas contended, .held only that a federal habeas court must determine whether the relevant state-court adjudication resulted in a “ ‘satisfactory conclusion.’ ” 505 U. S., at 287 (quoting Brown, 344 U. S., at 463). In Justice Thomas’ view, Brown did not answer “the question whether a ‘satisfactory’ conclusion was one that the habeas court considered *411correct, as opposed to merely reasonable .” 505 U. S., at 287 (emphases in original). In my separate opinion in Wright, I made the same distinction, maintaining that “a state court’s incorrect legal determination has [never] been allowed to stand because it was reasonable. We have always held that federal courts, even on habeas, have an independent obligation to say what the law is.” Id., at 305 (emphases added). In § 2254(d)(1), Congress specifically used the word “unreasonable,” and not a term like “erroneous” or “incorrect.” Under § 2254(d)(l)’s “unreasonable application” clause, then, a federal habeas court may not issue the writ simply because that court concludes in its independent judgment that the relevant state-court decision applied clearly established federal law erroneously or incorrectly. Rather, that application must also be unreasonable.

Justice Stevens turns a blind eye to the debate in Wright because he finds no indication in § 2254(d)(1) itself that Congress was “directly influenced” by Justice Thomas’ opinion in Wright. Ante, at 387-388, n. 14. As Justice Stevens himself apparently recognizes, however, Congress need not mention a prior decision of this Court by name in a statute’s text in order to adopt either a rule or a meaning given a certain term in that decision. See ante, at 380, n. 11. In any event, whether Congress intended to codify the standard of review suggested by Justice Thomas in Wright is beside the point. Wright is important for the light it sheds on §2254(d)(l)’s requirement that a federal habeas court inquire into the reasonableness of a state court’s application of clearly established federal law. The separate opinions in Wright concerned the very issue addressed by § 2254(d)(l)’s “unreasonable application” clause — whether, in reviewing a state-court decision on a state prisoner’s claims under federal law, a federal habeas court should ask whether the state-court decision was correct or simply whether it was reasonable. Justice Stevens’ claim that the debate in Wright concerned only the meaning of the Teague nonretro-*412activity rule is simply incorrect. See ante, at 387-388, n. 14. As even a cursory review of Justice Thomas’ opinion and my own opinion reveals, both the broader debate and the specific statements to which we refer, see supra, at 410-411, concerned precisely the issue of the standard of review to be employed by federal habeas courts. The Wright opinions confirm what § 2254(d)(l)’s language already makes clear— that an unreasonable application of federal law is different from an incorrect or erroneous application of federal law.

Throughout this discussion the meaning of the phrase “clearly established Federal law, as determined by the Supreme Court of the United States” has been put to the side. That statutory phrase refers to the holdings, as opposed to the dicta, of this Court’s decisions as of the time of the relevant state-court decision. In this respect, the “clearly established Federal law” phrase bears only a slight connection to our Teague jurisprudence. With one caveat, whatever would qualify as an old rule under our Teague jurisprudence will constitute “clearly established Federal law, as determined by the Supreme Court of the United States” under § 2254(d)(1). See, e. g., Stringer v. Black, 503 U. S. 222, 228 (1992) (using term “old rule”). The one caveat, as the statutory language makes clear, is that § 2254(d)(1) restricts the source of clearly established law to this Court’s jurisprudence.

In sum, § 2254(d)(1) places a new constraint on the power of a federal habeas court to grant a state prisoner’s application for a writ of habeas corpus with respect to claims adjudicated on the merits in state court. Under § 2254(d)(1), the writ may issue only if one of the following two conditions is satisfied — the state-court adjudication resulted in a decision that (1) “was contrary to ... clearly established Federal law, as determined by the Supreme Court of the United States,” or (2) “involved an unreasonable application of . . . clearly established Federal law, as determined by the Supreme Court of the United States.” Under the “contrary to” *413clause, a federal habeas court may grant the writ if the state court arrives at a conclusion opposite to that reached by this Court on a question of law or if the state court decides a case differently than this Court has on a set of materially indistinguishable facts. Under the “unreasonable application” clause, a federal habeas court may grant the writ if the state court identifies the correct governing legal principle from this Court’s decisions but unreasonably applies that principle to the facts of the prisoner’s case.

III

Although I disagree with Justice Stevens concerning the standard we must apply under § 2254(d)(1) in evaluating Terry Williams’ claims on habeas, I agree with the Court that the Virginia Supreme Court’s adjudication of Williams’ claim of ineffective assistance of counsel resulted in a decision that was both contrary to and involved an unreasonable application of this Court’s clearly established precedent. Specifically, I believe that the Court’s discussion in Parts III and IV is correct and that it demonstrates the reasons that the Virginia Supreme Court’s decision in Williams’ case, even under the interpretation of § 2254(d)(1) I have set forth above, was both contrary to and involved an unreasonable application of our precedent.

First, I agree with the Court that our decision in Strickland undoubtedly qualifies as “clearly established Federal law, as determined by the Supreme Court of the United States,” within the meaning of § 2254(d)(1). See ante, at 390-391. Second, I agree that the Virginia Supreme Court’s decision was contrary to that clearly established federal law to the extent it held that our decision in Lockhart v. Fretwell, 506 U. S. 364 (1993), somehow modified or supplanted the rule set forth in Strickland. See ante, at 391-395, 397. Specifically, the Virginia Supreme Court’s decision was contrary to Strickland itself, where we held that a defendant demonstrates prejudice by showing “that there is a reason*414able probability that, but for counsel's unprofessional errors, the result of the proceeding would have been different.” 466 U. S., at 694. The Virginia Supreme Court held, in contrast, that such a focus on outcome determination was insufficient standing alone. See Williams v. Warden of Mecklenburg Correctional Center, 254 Va. 16, 25, 27, 487 S. E. 2d 194, 199, 200 (1997). Lockhart does not support that broad proposition. As I explained in my concurring opinion in that case, “in the vast majority of cases ... [t]he determinative question — whether there is ‘a reasonable probability that, but for counsel's unprofessional errors, the result of the proceeding would have been different’ — remains unchanged.” 506 U. S., at 373 (quoting Strickland, 466 U. S., at 694). In his attempt to demonstrate prejudice, Williams did not rely on any “considerations that, as a matter of law, ought not inform the [prejudice] inquiry.” Lockhart, supra, at 373 (O’Connor, J., concurring). Accordingly, as the Court ably explains, the Virginia Supreme Court’s decision was contrary to Strickland.

To be sure, as The Chief Justice notes, post, at 417-418 (opinion concurring in part and dissenting in part), the Virginia Supreme Court did also inquire whether Williams had demonstrated a reasonable probability that, but for his trial counsel’s unprofessional errors, the result of his sentencing would have been different. See 254 Va., at 25-26, 487 S. E. 2d, at 199-200. It is impossible to determine, however, the extent to which the Virginia Supreme Court’s error with respect to its reading of Lockhart affected its ultimate finding that Williams suffered no prejudice. For example, at the conclusion of its discussion of whether Williams had demonstrated a reasonable probability of a different outcome at sentencing, the Virginia Supreme Court faulted the Virginia Circuit Court for its “emphasis on mere outcome determination, without proper attention to whether the result of the criminal proceeding was fundamentally unfair or unreliable.” 254 Va., at 27, 487 S. E. 2d, at 200.’ As the Court explains, *415however, see ante, at 393, Williams’ case did not implicate the unusual circumstances present in cases like Lockhart or Nix v. Whiteside, 475 U. S. 157 (1986). Accordingly, for the very reasons I set forth in my Lockhart concurrence, the emphasis on outcome was entirely appropriate in Williams’ case.

Third, I also agree with the Court that, to the extent the Virginia Supreme Court did apply Strickland, its application was unreasonable. See ante, at 395-398. As the Court correctly recounts, Williams’ trial counsel failed to conduct an investigation that would have uncovered substantial amounts of mitigation evidence. See ante, at 395-396. For example, speaking only of that evidence concerning Williams’ “nightmarish childhood,” ante, at 395, the mitigation evidence that trial counsel failed to present to the jury showed that “Williams’ parents had been imprisoned for the criminal neglect of Williams and his siblings, that Williams had been severely and repeatedly beaten by his father, that he had been committed to the custody of the social services bureau for two years during his parents’ incarceration (including one stint in an abusive foster home), and then, after his parents were released from prison, had been returned to his parents’ custody,” ibid, (footnote omitted). See also ante, at 395, n. 19. The consequence of counsel’s failure to conduct the requisite, diligent investigation into his client’s troubling background and unique personal circumstances manifested itself during his generic, unapologetic closing argument, which provided the jury with no reasons to spare petitioner’s life. More generally, the Virginia Circuit Court found that Williams’ trial counsel failed to present evidence showing that Williams “had a deprived and abused upbringing; that he may have been a neglected and mistreated child; that he came from an alcoholic family; . . . that he was borderline mentally retarded;” and that “[his] conduct had been good in certain structured settings in his life (such as when he was incarcerated).” App. 422-423. In addition, the Circuit *416Court noted the existence of “friends, neighbors and family of [Williams] who would have testified that he had redeeming qualities.” Id., at 42B. Based on its consideration of all of this evidence, the same trial judge that originally found Williams’ death sentence “ ‘justified and warranted,’ ” id., at 155, concluded that trial counsel’s deficient performance prejudiced Williams, id., at 424, and accordingly recommended that Williams be granted a new sentencing hearing, ibid. The Virginia Supreme Court’s decision reveals an obvious failure to consider the totality of the omitted mitigation evidence. See 254 Va., at 26, 487 S. E. 2d, at 200 (“At most, this evidence would have shown that numerous people, mostly relatives, thought that [Williams] was nonviolent and could cope very well in a structured environment”). For that reason, and the remaining factors discussed in the Court’s opinion, I believe that the Virginia Supreme Court’s decision “involved an unreasonable application of... clearly established Federal law, as determined by the Supreme Court of the United States.”

Accordingly, although I disagree with the interpretation of § 2254(d)(1) set forth in Part II of Justice Stevens’ opinion, I join Parts I, III, and IV of the Court’s opinion and concur in the judgment of reversal.

with whom Justice Scalia and Justice Thomas join, concurring in part and dissenting in part.

I agree with the Court’s interpretation of 28 U. S. C. § 2254(d)(1) (1994 ed., Supp. Ill), see ante, at 402-413 (opinion of O’Connor, J.), but disagree with its decision to grant ha-beas relief in this case.

There is “clearly established Federal law, as determined by [this Court]” that governs petitioner’s claim of ineffective assistance of counsel: Strickland v. Washington, 466 U. S. 668 (1984). Thus, we must determine whether the Virginia *417Supreme Court’s adjudication was “contrary to” or an “unreasonable application of” Strickland.

Generally, in an ineffective-assistance-of-counsel case where the state court applies Strickland, federal habeas courts can proceed directly to “unreasonable application” review. But, according to the substance of petitioner’s argument, this could be one of the rare cases where a state court applied the wrong Supreme Court precedent, and, consequently, reached an incorrect result. Petitioner argues, and the Court agrees, that the Virginia Supreme Court improperly held that Lockhart v. Fretwell, 506 U. S. 364 (1993), “modified or in some way supplanted” the rule set down in Strickland. See ante, at 391. I agree that such a holding would be improper. But the Virginia Supreme Court did not so hold as it did not rely on Lockhart to reach its decision.

Before delving into the evidence presented at the sentencing proceeding, the Virginia Supreme Court stated:

“We shall demonstrate that the criminal proceeding sentencing defendant to death was not fundamentally unfair or unreliable, and that the prisoner’s assertions about the potential effects of the omitted proof do not establish a ‘reasonable probability* that the result of the proceeding would have been different, nor any probability sufficient to undermine confidence in the outcome. Therefore, any ineffective assistance of counsel did not result in actual prejudice to the accused.” Williams v. Warden, 254 Va. 16, 25, 487 S. E. 2d 194, 199 (1997).

While the first part of this statement refers to Lockhart, the rest of the statement is straight out of Strickland. Indeed, after the initial allusion to Lockhart, the Virginia Supreme Court’s analysis explicitly proceeds under Strickland alone.* *418See 254 Va., at 26-27, 487 S. E. 2d, at 200. Because the Virginia Supreme Court did not rely on Lockhart to make its decision, and, instead, appropriately relied on Strickland, that court’s adjudication was not “contrary to” this Court’s clearly established precedent.

The question then becomes whether the Virginia Supreme Court’s adjudication resulted from an “unreasonable application of” Strickland. In my view, it did not.

I, like the Virginia Supreme Court and the Federal Court of Appeals below, -will assume without deciding that counsel’s performance fell below an objective standard of reasonableness. As to the prejudice inquiry, I agree with the Court of Appeals that evidence showing that petitioner presented a future danger to society was overwhelming. As that court stated:

“The murder of Mr. Stone was just one act in a crime spree that lasted most of Williams’s life. Indeed, the jury heard evidence that, in the months following the murder of Mr. Stone, Williams savagely beat an elderly woman, stole two cars, set fire to a home, stabbed a man during a robbery, set fire to the city jail, and confessed to having strong urges to choke other inmates and to break a fellow prisoner’s jaw.” 163 F. 3d 860, 868 (CA4 1998).

*419In Strickland, we said that both the performance and prejudice components of the ineffectiveness inquiry are mixed questions of law and fact. 466 U. S., at 698. It is with this kind of a question that the “unreasonable application of” clause takes on meaning. While the determination of “prejudice” in the legal sense may be a question of law, the subsidiary inquiries are heavily factbound.

Here, there was strong evidence that petitioner would continue to be a danger to society, both in and out of prison. It was not, therefore, unreasonable for the Virginia Supreme Court to decide that a jury would not have been swayed by evidence demonstrating that petitioner had a terrible childhood and a low IQ. See ante, at 395-396. The potential mitigating evidence that may have countered the finding that petitioner was a future danger was testimony that petitioner was not dangerous while in detention. See ante, at 396. But, again, it is not unreasonable to assume that the jury would have viewed this mitigation as unconvincing upon hearing that petitioner set fire to his cell while awaiting trial for the murder at hand and has repeated visions of harming other inmates.

Accordingly, I would hold that habeas relief is barred by 28 U. S. C. § 2254(d) (1994 ed., Supp. III).