delivered the opinion of the Court.

This is a civil antitrust case brought by the United States to nullify an association’s canon of ethics prohibiting competitive bidding by its members. The question is whether the canon 'may be justified under the Sherman Act, 26 Stat. 209, as amended, 15 U. S. C. § 1 et seq. (1976 ed.), because it was adopted by members of a learned profession for the purpose of minimizing the risk that competition would produce inferior engineering work endangering the public safety. The District Court rejected this justification without making any findings on the likelihood that competition would produce the dire consequences foreseen by the association.1 The Court of Appeals affirmed.2 We granted certiorari to decide whether the District Court should have considered the factual basis for the proffered justification before rejecting it. 434 U. S. 815. Because we are satisfied that the asserted defense rests on a fundamental misunderstanding of the Rule of Reason frequently applied in antitrust litigation, we affirm.

I

Engineering is an important and learned profession. There are over 750,000 graduate engineers in the United States, of whom about 325,000 are registered as professional engineers. Registration requirements vary from State to State, but usually require the applicant to be a graduate engineer with at least *682four years of practical experience and to pass a written examination. About half of those who are registered engage in consulting engineering on a fee basis. They perform services in connection with the study, design, and construction of all types of improvements to real property — bridges, office buildings, airports, and factories are examples. Engineering fees, amounting to well over $2 billion each year, constitute about 5% of total construction costs. In any given facility, approximately 50% to 80% of the cost of construction is the direct result of work performed by an engineer concerning the systems and equipment to be incorporated in the structure.

The National Society of Professional Engineers (Society) was organized in 1935 to deal with the nontechnical aspects of engineering practice, including the promotion of the professional, social, and economic interests of its members. Its present membership of 69,000 resides throughout the United States and in some foreign countries. Approximately 12,000 members are consulting engineers who offer their services to governmental, industrial, and private clients. Some Society members are principals or chief executive officers of some of the largest engineering firms in the country.

The charges of a consulting engineer may be computed in different ways. He may charge the client a percentage of the cost of the project, may set his fee at his actual cost plus overhead plus a reasonable profit, may charge fixed rates per hour for different types of work, may perform an assignment for a specific sum, or he may combine one or more of these approaches. Suggested fee schedules for particular types of services in certain areas have been promulgated from time to time by various local societies. This case does not, however, involve any claim that the National Society has tried to fix specific fees, or even a specific method of calculating fees. It involves a charge that the members of the Society have unlawfully agreed to refuse to negotiate or even to discuss the question of fees until after a prospective client has selected the *683engineer for a particular project. Evidence of this agreement is found in § 11 (c) of the Society’s Code of Ethics, adopted in July 1964.3

The District Court found that the Society’s Board of Ethical Review has uniformly interpreted the “ethical rules against competitive bidding for engineering services as prohibiting the submission of any form of price information to a prospective customer which would enable that customer to make a price comparison on engineering services.” 4 If the client requires that such information be provided, then § 11 (c) imposes an *684obligation upon the engineering firm to withdraw from consideration for that job. The Society’s Code of Ethics thus “prohibits engineers from both soliciting and submitting such price information,” 389 F. Supp. 1193, 1206 (DC 1974),5 and seeks to preserve the profession’s “traditional” method of selecting professional engineers. Under the traditional method, the client initially selects an engineer on the basis of background and reputation, not price.6

In 1972 the Government filed its complaint against the Society alleging that members had agreed to abide by canons of ethics prohibiting the submission of competitive bids for engineering services and that, in consequence, price competition among the members had been suppressed and customers had been deprived of the benefits of free and open competition. The complaint prayed for an injunction terminating the unlawful agreement.

In its answer the Society admitted the essential facts alleged by the Government and pleaded a series of affirmative defenses, only one of which remains in issue. In that defense, the Society averred that the standard set out in the Code of Ethics was reasonable because competition among professional engineers was contrary to the public interest. It was averred that it would be cheaper and easier for an engineer “to design and specify inefficient and unnecessarily expensive structures and *685methods of construction.” 7 Accordingly, competitive pressure to offer engineering services at the lowest possible price would adversely affect the quality of engineering. Moreover, the practice of awarding engineering contracts to the lowest bidder, regardless of quality, would be dangerous to the public health, safety, and welfare. For these reasons, the Society claimed that its Code of Ethics was not an “unreasonable restraint of interstate trade or commerce.”

The parties compiled a voluminous discovery and trial record. The District Court made detailed findings about the *686engineering profession, the Society, its members’ participation in interstate commerce, the history of the ban on competitive bidding, and certain incidents in which the ban appears to have been violated or enforced. The District Court did not, however, make any finding on the question whether, or to what extent, competition had led to inferior engineering work which, in turn, had adversely affected the public health, safety, or welfare. That inquiry was considered unnecessary because the court was convinced that the ethical prohibition against competitive bidding was “on its face a tampering with the price structure of engineering fees in violation of § 1 of the Sherman Act.” 389 F. Supp., at 1200.

Although it modified the injunction entered by the District Court,8 the Court of Appeals affirmed its conclusion that the agreement was unlawful on its face and therefore “illegal without regard to claimed or possible benefits.” 181 U. S. App. D. C. 41, 47, 556 F. 2d 978, 984.

II

In Goldfarb v. Virginia State Bar, 421 U. S. 773, the Court held that a bar association’s rule prescribing minimum fees for legal services violated § 1 of the Sherman Act. In that opinion the Court noted that certain practices by members of a learned profession might survive scrutiny under the Rule of Reason even though they would be viewed as a violation of the Sherman Act in another context. The Court said:

“The fact that a restraint operates upon a profession as distinguished from a business is, of course, relevant in determining whether that particular restraint violates the *687Sherman Act. It would be unrealistic to view the practice of professions as interchangeable with other business activities, and automatically to apply to the professions antitrust concepts which originated in other areas. The public service aspect, and other features of the professions may require that a particular practice, which could properly be viewed as a violation of the Sherman Act in another context, be treated differently. We intimate no view on any other situation than the one with which we are confronted today.” 421 U. S., at 788-789, n. 17.

Relying heavily on this footnote, and on some of the major cases applying a Rule of Reason — principally Mitchel v. Reynolds, 1 P. Wms. 181, 24 Eng. Rep. 347 (1711); Standard Oil Co. v. United States, 221 U. S. 1; Chicago Board of Trade v. United States, 246 U. S. 231; and Continental T. V., Inc. v. GTE Sylvania Inc., 433 U. S. 36 — petitioner argues that its attempt to preserve the profession’s traditional method of setting fees for engineering services is a reasonable method of forestalling the public harm which might be produced by unrestrained competitive bidding. To evaluate this argument it is necessary to identify the contours of the Rule of Reason and to discuss its application to the kind of justification asserted by petitioner.

A. The Rule of Reason.

One problem presented by the language of § 1 of the Sherman Act is that it cannot mean what it says. The statute says that “every” contract that restrains trade is unlawful.9 But, as Mr. Justice Brandéis perceptively noted, restraint is the very *688essence of every contract;10 read literally, § 1 would outlaw the entire body of private contract law. Yet it is that body of law that establishes the enforceability of commercial agreements and enables competitive markets — indeed, a competitive economy — to function effectively.

Congress, however, did not intend the text of the Sherman Act to delineate the full meaning of the statute or its application in concrete situations. The legislative history makes it perfectly clear that it expected the courts to give shape to the statute’s broad mandate by drawing on common-law tradition.11 The Rule of Reason, with its origins in common-law precedents long antedating the Sherman Act, has served that purpose. It has been used to give the Act both flexibility and definition, and its central principle of antitrust analysis has remained constant. Contrary to its name, the Rule does not open the field of antitrust inquiry to any argument in favor of a challenged restraint that may fall within the realm of reason. Instead, it focuses directly on the challenged restraint’s impact on competitive conditions.

This principle is apparent in even the earliest of cases applying the Rule of Reason, Mitchel v. Reynolds, supra. Mitchel involved the enforceability of a promise by the seller of a bakery that he would not compete with the purchaser of his business. The covenant was for a limited time and applied only to the area in which the bakery had operated. It was therefore upheld as reasonable, even though it deprived the *689public of the benefit of potential competition. The long-run benefit of enhancing the marketability of the business itself — and thereby providing incentives to develop such an enterprise — outweighed the temporary and limited loss of competition.12

The Rule of Reason suggested by Mitchel v. Reynolds has been regarded as a standard for testing the enforceability of covenants in restraint of trade which are ancillary to a legitimate transaction, such as an employment contract or the sale of a going business. Judge (later Mr. Chief Justice) Taft so interpreted the Rule in his classic rejection of the argument that competitors may lawfully agree to sell their goods at the same price as long as the agreed-upon price is reasonable. United States v. Addyston Pipe & Steel Co., 85 F. 271, 282-283 (CA6 1898), aff'd, 175 U. S. 211. That case, and subsequent decisions by this Court, unequivocally foreclose an interpretation of the Rule as permitting an inquiry into the reasonableness of the prices set by private agreement.13

The early cases also foreclose the argument that because of the special characteristics of a particular industry, monopolistic arrangements will better promote trade and commerce than competition. United States v. Trans-Missouri Freight Assn., 166 U. S. 290; United States v. Joint Traffic Assn., 171 U. S. 505, 573-577. That kind of argument is properly addressed to Congress and may justify an exemption from the statute for *690specific industries,14 but it is not permitted by the Rule of Reason. As the Court observed in Standard Oil Co. v. United States, 221 U. S., at 65, “restraints of trade within the purview of the statute . . . [can]not be taken out of that category by indulging in general reasoning as to the expediency or non-expediency of having made the contracts or the wisdom or want of wisdom of the statute which prohibited their being made.” The test prescribed in Standard Oil is whether the challenged contracts or acts “were unreasonably restrictive of competitive conditions.” Unreasonableness under that test could be based either (1) on the nature or character of the contracts, or (2) on surrounding circumstances giving rise to the inference or presumption that they were intended to restrain trade and enhance prices.15 Under either branch of the test, the inquiry is confined to a consideration of impact on competitive conditions.16

*691In this respect the Rule of Reason has remained faithful to its origins. From Mr. Justice Brandéis’ opinion for the Court in Chicago Board of Trade to the Court opinion written by Mr. Justice Powell in Continental T. V., Inc., the Court has adhered to the position that the inquiry mandated by the Rule of Reason is whether the challenged agreement is one that promotes competition or one that suppresses competition. “The true test of legality is whether the restraint imposed is such as merely regulates and perhaps thereby promotes competition or whether it is such as may suppress or even destroy competition.” 246 U. S., at 238, quoted in 433 U. S., at 49 n. 15.17

*692There are, thus, two complementary categories of antitrust analysis. In the first category are agreements whose nature and necessary effect are so plainly anticompetitive that no elaborate study of the industry is needed to establish their illegality — they are “illegal per se." In the second category are agreements whose competitive effect can only be evaluated by analyzing the facts peculiar to the business, the history of the restraint, and the reasons why it was imposed. In either event, the purpose of the analysis is to form a judgment about the competitive significance of the restraint; it is not to decide whether a policy favoring competition is in the public interest, or in the interest of the members of an industry. Subject to exceptions defined by statute, that policy decision has been made by the Congress.18

B. The Ban on Competitive Bidding.

Price is the “central nervous system of the economy,” United States v. Socony-Vacuum Oil Co., 310 U. S. 150, 226 n. 59, and an agreement that “interfere[s] with the setting of price by free market forces” is illegal on its face. United States v. Container Corp., 393 U. S. 333, 337. In this case we are presented with an agreement among competitors to refuse to discuss prices with potential customers until after negotiations have" resulted in the initial selection of an engineer. While this is not price fixing as such, no elaborate industry analysis is required to demonstrate the anticompetitive character of such an agreement. It operates as an absolute ban on competitive bidding, applying with equal force to both complicated and simple projects and to both inexperienced and sophisticated customers. As the District Court found, the ban “impedes the ordinary give and take of the market place,” and substantially deprives the customer of “the ability to utilize *693and compare prices in selecting engineering services.” 404 F. Supp. 457, 460. On its face, this agreement restrains trade within the meaning of § 1 of the Sherman Act.

The Society’s affirmative defense confirms rather than refutes the anticompetitive purpose and effect of its agreement. The Society argues that the restraint is justified because bidding on engineering services is inherently imprecise, would lead to deceptively low bids, and would thereby tempt individual engineers to do inferior work with consequent risk to public safety and health.19 The logic of this argument rests on the assumption that the agreement will tend to maintain the price level; if it had no such effect, it would not serve its intended purpose. The Society nonetheless invokes the Rule of Reason, arguing that its restraint on price competition ultimately inures to the public benefit by preventing the *694production of inferior work and by insuring ethical behavior. As the preceding discussion of the Rule of Reason reveals, this Court has never accepted such an argument.

It may be, as petitioner argues, that competition tends to force prices down and that an inexpensive item may be inferior to one that is more costly. There is some risk, therefore, that competition will cause some suppliers to market a defective product. Similarly, competitive bidding for engineering projects may be inherently imprecise and incapable of taking into account all the variables which will be involved in the actual performance of the project.20 Based on these considerations, a purchaser might conclude that his interest in quality — which may embrace the safety of the end product — outweighs the advantages of achieving cost savings by pitting one competitor against another. Or an individual vendor might independently refrain from price negotiation until he has satisfied himself that he fully understands the scope of his customers’ needs. These decisions might be reasonable; indeed, petitioner has provided ample documentation for that thesis. But these are not reasons that satisfy the Rule; nor are such individual decisions subject to antitrust attack.

The Sherman Act does not require competitive bidding;21 *695it prohibits unreasonable restraints on competition. Petitioner’s ban on competitive bidding prevents all customers from making price comparisons in the initial selection of an engineer, and imposes the Society’s views of the costs and benefits of competition on the entire marketplace. It is this restraint that must be justified under the Rule of Reason, and petitioner’s attempt to do so on the basis of the potential threat that competition poses to the public safety and the ethics of its profession is nothing less than a frontal assault on the basic policy of the Sherman Act.

The Sherman Act reflects a legislative judgment that ultimately competition will produce not only lower prices, but also better goods and services. “The heart of our national economic policy long has been faith in the value of competition.” Standard Oil Co. v. FTC, 340 U. S. 231, 248. The assumption that competition is the best method of allocating resources in a free market recognizes that all elements of a bargain— quality, service, safety, and durability — and not just the immediate cost, are favorably affected by the free opportunity to select among alternative offers. Even assuming occasional exceptions to the presumed consequences of competition, the statutory policy precludes inquiry into the question whether competition is good or bad.

The fact that engineers are often involved in large-scale projects significantly affecting the public safety does not alter our analysis. Exceptions to the Sherman Act for potentially dangerous goods and services would be tantamount to a repeal of the statute. In our complex economy the number of items that may cause serious harm is almost endless — automobiles, drugs, foods, aircraft components, heavy equipment, and countless others, cause serious harm to individuals or to the public at large if defectively made. The judiciary cannot *696indirectly protect the public against this harm by conferring monopoly privileges on the manufacturers.

By the same token, the cautionary footnote in Goldfarb, 421 U. S., at 788-789, n. 17, quoted supra, cannot be read as fashioning a broad exemption under the Rule of Reason for learned professions. We adhere to the view expressed in Goldfarb that, by their nature, professional services may differ significantly from other business services, and, accordingly, the nature of the competition in such services may vary. Ethical norms may serve to regulate and promote this competition, and thus fall within the Rule of Reason.22 But the Society’s argument in this case is a far cry from such a position. We are faced with a contention that a total ban on competitive bidding is necessary because otherwise engineers will be tempted to submit deceptively low bids. Certainly, the problem of professional deception is a proper subject of an ethical canon. But, once again, the equation of competition with deception, like the similar equation with safety hazards, is simply too broad; we may assume that competition is not entirely conducive to ethical behavior, but that is not a reason, cognizable under the Sherman Act, for doing away with competition.

In sum, the Rule of Reason does not support a defense based on the assumption that competition itself is unreasonable. Such a view of the Rule would create the “sea of doubt” on which Judge Taft refused to embark in Addyston, 85 F., at 284, and which this Court has firmly avoided ever since.

Ill

The judgment entered by the District Court, as modified by *697the Court of Appeals,23 prohibits the Society from adopting any official opinion, policy statement, or guideline stating or implying that competitive bidding is unethical.24 Petitioner argues that this judgment abridges its First Amendment rights.25 We find no merit in this contention.

Having found the Society guilty of a violation of the Sherman Act, the District Court was empowered to fashion appropriate restraints on the Society’s future activities both to avoid a recurrence of the violation and to eliminate its consequences. See, e. g., International Salt Co. v. United States, 332 U. S. 392, 400-401; United States v. Glaxo Group, Ltd., 410 U. S. 52, 64. While the resulting order may curtail the exercise of liberties that the Society might otherwise enjoy, that is a necessary and, in cases such as this, unavoidable consequence of the violation. Just as an injunction against price fixing abridges the freedom of businessmen to talk to one another about prices, so too the injunction in this case must restrict the Society’s range of expression on the ethics of competitive bidding.26 The First Amendment does not “make it . . . impossible ever to enforce laws against agreements in restraint of trade . . . .” Giboney v. Empire Storage & Ice Co., 336 U. S. 490, 502. In fashioning a remedy, the District Court may, of course, consider the fact that its injunction may impinge upon rights that would otherwise be constitutionally *698protected, but those protections do not prevent it from remedying the antitrust violations.

The standard against which the order must be judged is whether the relief represents a reasonable method of eliminating the consequences of the illegal conduct. We agree with the Court of Appeals that the injunction, as modified, meets this standard. While it goes beyond a simple proscription against the precise conduct previously pursued, that is entirely appropriate.

“The District Court is not obliged to assume, contrary to common experience, that a violator of the antitrust laws will relinquish the fruits of his violation more completely than the court requires him to do. And advantages already in hand may be held by methods more subtle and informed, and more difficult to prove, than those which, in the first place, win a market. When the purpose to restrain trade appears from a clear violation of law, it is not necessary that all of the untraveled roads to that end be left open and that only the worn one be closed.” International Salt Co., supra, at 400.

The Society apparently fears that the District Court’s injunction, if broadly read, will block legitimate paths of expression on all ethical matters relating to bidding.27 But the answer to these fears is, as the Court held in International Salt, that the burden is upon the proved transgressor “to bring any proper claims for relief to the court’s attention.” Ibid. In *699this case, the Court of Appeals specifically stated that “[i]f the Society wishes to adopt some other ethical guideline more closely confined to the legitimate objective of preventing deceptively low bids, it may move the district court for modification of the decree.” 181 U. S. App. D. C., at 46, 555 F. 2d, at 983. This is, we believe, a proper approach, adequately protecting the Society’s interests. We therefore reject petitioner’s attack on the District Court’s order.

The judgment of the Court of Appeals is

Affirmed.

with whom Mr. Justice Rehnquist joins, concurring in part and concurring in the judgment.

I join Parts I and III of the Court’s opinion and concur in the judgment. I do not join Part II because I would not, at least for the moment, reach as far as the Court appears to me to do in intimating, ante, at 696, and n. 22, that any ethical rule with an overall anticompetitive effect promulgated by a professional society is forbidden under the Sherman Act. In my view, the decision in Goldfarb v. Virginia State Bar, 421 U. S. 773, 788-789, n. 17 (1975), properly left to the Court some flexibility in considering how to apply traditional Sherman Act concepts to professions long consigned to self-regulation. Certainly, this case does not require us to decide whether the “Rule of Reason” as applied to the professions ever could take account of benefits other than increased competition. For even accepting petitioner’s assertion that product quality is one such benefit, and that maintenance of the quality of engineering services requires that an engineer not bid before he has made full acquaintance with the scope of a client’s desired project, Brief for Petitioner 49-50, 54, petitioner Society’s rule is still grossly overbroad. As petitioner concedes, Tr. of Oral *700Arg. 47-48, § 11 (c) forbids any simultaneous consultation between a client and several engineers, even where the client provides complete information to each about the scope and nature of the desired project before requesting price information. To secure a price estimate on a project, the client must purport to engage a single engineer, and so long as that engagement continues no other member of the Society is permitted to discuss the project with the client in order to provide comparative price information. Though § 11 (c) does not fix prices directly, and though the customer retains the option of rejecting a particular engineer’s offer and beginning negotiations all over again with another engineer, the forced process of sequential search inevitably increases the cost of gathering price information, and hence will dampen price competition, without any calibrated role to play in preventing uninformed bids. Then, too, the Society’s rule is overbroad in the aspect noted by Judge Leventhal, when it prevents any dissemination of competitive price information in regard to real property improvements prior to the engagement of a single engineer regardless of “the sophistication of the purchaser, the complexity of the project, or the procedures for evaluating price information.” 181 U. S. App. D. C. 41, 45, 555 F. 2d 978, 982 (1977).

My skepticism about going further in this case by shaping the Rule of Reason to such a narrow last as does the majority,* arises from the fact that there may be ethical rules which have a more than de minimis anticompetitive effect and yet are important in a profession’s proper ordering. A medical association’s prescription of standards of minimum competence for licensing or certification may lessen the number of *701entrants. A bar association’s regulation of the permissible forms of price advertising for nonroutine legal services or limitation of in-person solicitation, see Bates v. State Bar of Arizona, 433 U. S. 350 (1977), may also have the effect of reducing price competition. In acknowledging that “professional services may differ significantly from other business services” and that the “nature of the competition in such services may vary,” ante, at 696, but then holding that ethical norms can pass muster under the Rule of Reason only if they promote competition, I am not at all certain that the Court leaves enough elbowroom for realistic application of the Sherman Act to professional services.

concurring in part and dissenting in part.

I concur in the Court’s judgment to the extent it sustains the finding of a violation of the Sherman Act but dissent from that portion of the judgment prohibiting petitioner from stating in its published standards of ethics the view that competitive bidding is unethical. The First Amendment guarantees the right to express such a position and that right cannot be impaired under the cloak of remedial judicial action.