In the USA, private plaintiffs can sue for antitrust violations under both federal and state law, and private parties continue to actively pursue lawsuits in the technology, healthcare and other industries. Recent important antitrust cases include the following.

• In Chalmers v NCAA, Judge Claudia Wilken from the Northern District of California approved the USD2.8 billion settlement in favour of former Division I student-athletes who alleged that the National Collegiate Athletic Association (NCAA) prevented plaintiffs from profiting from their own personal brand while in college due to the NCAA’s control of athletes’ name, image and likeness (NIL) rights.
• In Regeneron v Amgen, a jury returned a verdict and award of USD407 million in damages for Regeneron Pharmaceuticals, Inc, after finding Amgen, Inc liable for antitrust and tort violations by creating a cross-therapeutic bundled rebate scheme.
• In Epic v Apple, Epic Games filed a complaint against Apple in August 2020, alleging that Apple engaged in anti-competitive practices, which resulted in a permanent injunction to restrain Apple’s monopolisation of the iOS app distribution market and the in-app payment processing market. Apple has now been found in “wilful violation” of the injunction and in civil contempt for perjury and abuse of attorney-client privilege to delay proceedings.
• In International Construction Products v Caterpillar, the plaintiff alleged that Caterpillar tortiously interfered with a contract between International Construction Products (ICP) and IronPlanet. While a jury originally awarded ICP USD100 million in damages, in March 2025 a district judge vacated the entire award for damages, ruling that ICP failed to provide sufficient evidence of actual damages.

In recent years, US antitrust authorities and private plaintiffs have aggressively challenged proposed mergers and alleged anti-competitive practices in a wide array of industries. Many recent notable cases have either found antitrust violations or resulted in settlements. In addition to the private cases discussed in 1.1 Current Framework for Private Antitrust Litigation, US antitrust authorities have brought several cases as well. In FTC v Meta, the federal district court ruled that the Federal Trade Commission’s (FTC) claim against Meta, for allegedly monopolising the personal social media networking market through its acquisitions of Instagram and WhatsApp, was plausible. A six-week bench trial followed, which concluded in May 2025.

Furthermore, in United States v Google (including both advertising technology and search-related cases), a district judge held that Google “violated Section 2 of the Sherman Act by wilfully acquiring and maintaining monopoly power” in the open-web display publisher ad server market and exchange market. Additionally, several states have recently adopted their own form of pre-merger notification requirements.

Legislative developments are discussed further in 13.1 Legislative Trends and Other Developments.

Section 4 of the Clayton Act authorises damages suits in federal court by “any person” – which includes corporations and other legal entities – “who shall be injured in his business or property by reason of anything forbidden in the antitrust laws” (15 USC Sections 7; 15[a]). The federal antitrust laws underlying private damages claims include, perhaps most prominently, Section 1 of the Sherman Antitrust Act (prohibiting concerted action that unreasonably restrains trade) and Section 2 (prohibiting single-firm conduct that maintains or creates a dominant position by unreasonably excluding competitors from a market). State antitrust laws vary, but broadly confer private rights of action on a similar basis.

The Clayton Act allows litigants to pursue damages claims that follow on from parallel scrutiny by federal law enforcement and standalone claims. Standalone claims – brought by private litigants in the absence of any governmental action against the defendants – are common in US practice. News that antitrust authorities are investigating potential anti-competitive conduct commonly prompts private litigants to quickly initiate parallel damages actions, usually while the underlying investigation remains pending.

Most federal competition matters are resolved in the US federal courts, which have exclusive jurisdiction over federal antitrust claims. An exception is the administrative adjudicatory process carried out by the FTC (see 2.3 Impact of Competition Authorities). The Clayton Act accords plaintiffs wide latitude in choosing a venue (that is, the US federal district court in which they file suit). Venue is proper under the Clayton Act in any federal district where the defendant “resides or is found or has an agent”, or “transacts business” (15 USC Sections 15[a], 22).

The parties may request, or the court may on its own decide, “for the convenience of parties and witnesses” or “in the interest of justice”, to transfer a federal antitrust litigation to a different federal district where the case “might have been brought” or to any district to which “all parties have consented” (28 USC Section 1404[a]).

Different claimants may file parallel antitrust complaints in differing federal districts. When this occurs, the parties may request that the Judicial Panel on Multidistrict Litigation consolidate claims – involving “common questions of fact” – into a single federal district for co-ordinated pretrial proceedings (28 USC Section 1407[a]).

Antitrust claims made under state law may also be heard in federal court if:

• they supplement a federal claim (28 USC Section 1367);
• the parties reside in different jurisdictions (28 USC Section 1332[a]); or
• they meet the requirements of the Class Action Fairness Act of 2005, which significantly expanded the federal courts’ authority to resolve large class actions even if pursued under state law (28 USC Section 1332[d]).

The federal antitrust enforcement agencies exercise independent judgement over which matters to litigate, but their enforcement actions are subject to judicial review in some form. The FTC, as an independent administrative agency, possesses the statutory authority to adjudicate civil claims of “unfair competition” before the agency’s own administrative law judges in trial-type proceedings. Decisions by FTC administrative judges are automatically reviewed by the FTC commissioners, and a losing defendant may appeal the Commission’s decision to the federal appellate courts.

By contrast, the US Department of Justice, Antitrust Division (the “Division”), as a law enforcement agency, lacks the authority to adjudicate its own disputes, and instead must pursue enforcement actions exclusively in the federal courts. The courts likewise retain oversight of Division settlements of these cases before trial. When the Division concludes a civil antitrust investigation or litigation by settlement (known as a consent decree), the Antitrust Procedures and Penalties Act obliges the Division to file a complaint and proposed settlement materials in federal court and to seek judicial approval of the settlement’s terms. However, the court’s review is limited to ensuring that the settlement is in the “public interest” (15 USC Section 16).

By contrast, a criminal antitrust prosecution – which, as a matter of policy, the Division uses to target only “hardcore” per se competition offences – is overseen in its initial stages by a federal grand jury, which decides whether there is “probable cause” to believe a crime was committed, justifying the issuance of an indictment. In general, criminal antitrust defendants often plead guilty rather than stand trial. In that circumstance, the trial court has discretion to accept or reject the Division’s recommended sentence.

Consequences of Federal Antitrust Enforcement Actions

A federal antitrust enforcement action can have important consequences for parallel private litigation. For example, a final judgment or decree against a defendant in a federal antitrust enforcement action can serve as prima facie evidence against that defendant in related private litigation (15 USC Section 16[a]). In addition, the Division periodically intervenes in civil antitrust litigation to request a stay of discovery where the Division believes the exchange of evidence between the parties could undermine the Division’s ongoing criminal investigation of one or more defendants. Finally, the Division and the FTC may intervene in private antitrust litigation as an amicus curiae to offer their views on the application of the antitrust laws to a given complaint.

Section 4 of the Clayton Act requires a plaintiff to prove that the defendant(s) violated the antitrust laws and that the plaintiff has been “injured in his business or property” – that is, suffered economic loss – “by reason of” that violation (15 USC Section 15). Plaintiffs in federal antitrust cases must prove each element of their claim by a “preponderance of the evidence” – meaning they must establish through direct or circumstantial evidence that a fact is more likely than not true.

Defendants in federal antitrust litigation cannot escape liability by establishing that direct purchasers passed on to indirect purchasers some or all of an anti-competitive overcharge (Hanover Shoe v United Shoe Mach, 392 US 481 [1968]). However, several state antitrust laws authorising antitrust claims by indirect purchasers provide that courts should take steps to avoid duplicative recovery, including by apportioning damages between direct and indirect purchasers (as discussed in 4.3 Direct/Indirect Purchasers).

A private litigant may pursue a claim for damages under the federal antitrust laws within four years after the cause of action has “accrued” (15 USC Section 15b). An antitrust claim accrues when the defendants’ offending conduct causes the claimant to suffer a non-speculative injury. In the case of an ongoing conspiracy, the limitations period runs from each new “overt act” in furtherance of the conspiracy that inflicts new and accumulating injuries on the plaintiff (Zenith Radio Corp v Hazeltine Research, 401 US 321 [1971]). In some cases, the theory of “fraudulent concealment” may equitably “toll” (ie, pause) the limitations period where defendants have taken affirmative actions to prevent a plaintiff from learning of their cause of action.

The limitations period for private litigants can also be tolled for other statutory reasons, such as a pending government action for the same conduct (15 USC Section 16[i]). In addition, the statute of limitations for a plaintiff who opts out of a purported class action remains tolled during pendency of the class claim (American Pipe & Construction v Utah, 414 US 538 [1974]). In 2018, the Supreme Court clarified that this rule applies only to opt-out plaintiffs who seek to pursue damages claims on their own behalf, and not to plaintiffs who seek to re-assert class claims after a prior class has failed to achieve certification for the same issues (China Agritech v Resh, 138 S Ct 1800 [2018]).

Limitations periods under state antitrust laws vary from as little as one year to as much as six years, with four years being the most common. A small handful of states do not specify a limitations period for antitrust claims.

The duration of federal antitrust litigation varies dramatically. Most cases are dismissed or resolved before trial. Cases can be dismissed at the pleadings stage with reasonable speed, though claimants may be permitted to re-plead their allegations, and may appeal dismissal. Cases that survive the dismissal stage can go on for years, as the parties exchange evidence, retain experts, dispute class certification (see 4.4 Class Certification) and seek summary judgment before trial.

Class actions are at the heart of private antitrust litigation in the USA. Any plaintiff suing under the federal antitrust laws may seek to pursue their claims on behalf of a putative class of parties whose injuries at the hands of defendants involve the same set of concerns. To maintain a class, a plaintiff must move for “class certification”, establishing by a preponderance of the evidence that the class complies with the requirements of US Federal Rule of Civil Procedure 23 (see 4.4 Class Certification).

Class litigation typically proceeds on an “opt-out” basis: members of a “certified” class are included in the resolution of the claim unless they affirmatively opt to be excluded.

The US Supreme Court has ruled that “indirect purchasers” – consumers who do not purchase directly from defendants, but to whom the direct purchaser has passed on the overcharge caused by the defendants’ conspiracy – generally lack standing to pursue damages claims under the federal antitrust laws (Illinois Brick v Illinois, 431 US 720 [1977]). This decision is rooted in concerns for judicial economy and the challenges in apportioning damages passed from direct to indirect purchasers (and the threat that those challenges could lead to duplicative recovery).

There are exceptions to this rule, including when the direct purchaser is a party to the conspiracy. Further, since the Supreme Court announced the bar on federal indirect purchaser claims, most states have enacted what are known as Illinois Brick repealer statutes, which sanction indirect claims under state law. As a result, antitrust defendants may be forced to litigate in a single federal court both against direct purchasers under federal law and against indirect purchasers under various state laws.

Although there have been calls for Congress to overturn the Illinois Brick rule, it has not done so. Additionally, the US Supreme Court affirmed Illinois Brick’s bar on damages suits by indirect purchasers in 2019 – the Court’s first application of the rule to a digital market (Apple v Pepper, 139 S Ct 1514 [2019]).

More generally, the US Supreme Court has articulated important “limiting contours” on the right of private plaintiffs to recover damages under the antitrust laws, embodied in the requirement that plaintiffs establish the element of “antitrust standing”, which tests whether a particular plaintiff is the appropriate party to recover damages for an established antitrust violation. First, antitrust plaintiffs must demonstrate that they have suffered an “antitrust injury” – that is, an injury “of the type the antitrust laws were intended to prevent” (Brunswick v Pueblo Bowl-O-Mat, 429 US 477 [1977]). For example, a retailer that loses its distribution agreement with a manufacturer for refusing to conspire with other retailers to rig bids to sell the manufacturer’s products has not suffered antitrust injury. This is because the retailer’s harm (lost profits) does not “flow... from that which makes bid-rigging unlawful” under the antitrust laws (ie, higher prices to consumers) (Gatt Communications v PMC Associates, 711 F 3d 68 [2d Cir 2013]).

Plaintiffs must also establish that they are “efficient enforcers of the antitrust laws”, an inquiry that assesses (among other things) the “directness” of the link between the asserted conduct and injury, and the existence of other “more direct” victims (Associated General Contractors of California v California State Council of Carpenters, 459 US 519 [1983]). These elements are not part of the government’s burden in proving an antitrust violation.

Class-certification review involves a “rigorous analysis” that “will frequently entail overlap with the merits of the plaintiff’s underlying claim” (Comcast v Behrend, 569 US 27, 34 [2013]). To begin with, a plaintiff must affirmatively demonstrate that:

• the class is so “numerous” that simple “joinder” of each class member’s individual complaints into a single litigation would be “impracticable”;
• the class members present questions of law or fact in “common” with one another (ie, that they have suffered the same injury);
• the lead plaintiff’s claims are “typical” of those of the class; and
• the lead plaintiff will “fairly and adequately protect the interests of the class” (Fed R Civ P 23[a]).

In addition to those “prerequisites”, a plaintiff must also establish that the putative class meets one of several enumerated bases for certification. Most antitrust class actions seek to proceed on the showing that both common questions of law or fact “predominate” over questions affecting individual members and a class action is “superior” to alternative methods of “fairly and efficiently adjudicating the controversy” (Fed R Civ P 23[b][3]).

In addition to the venue requirements of the Clayton Act (see 2.2 Courts), plaintiffs must establish that both the defendant(s) and the conduct complained of are subject to the jurisdiction of the US courts. These requirements include both personal and subject matter jurisdiction.

Personal Jurisdiction

Personal jurisdiction assesses the court’s power to hear cases against particular defendants. As a matter of constitutional due process, the federal courts can only impose liability on defendants that have sufficient “minimum contacts” with the forum state. Depending on the strength of a defendant’s forum contacts, personal jurisdiction can be general (all-purpose) or specific (conduct-linked). For corporations, in all but the most “exceptional” cases, general jurisdiction will exist only if the defendant is headquartered or incorporated in the forum (Daimler v Bauman, 571 US 117 [2014]).

Specific jurisdiction, which is narrower, is appropriate only for claims that “arise out of or relate to” a foreign defendant’s own purposeful contacts with the forum itself (and not just contacts with parties that reside in the forum) (Walden v Fiore, 571 US 277 [2014]). Plaintiffs must also have suffered an injury in the forum, although injury alone is not enough (Bristol-Myers Squibb v Superior Court of California, San Francisco County, 582 US 255 [2017]). The Supreme Court has recently reiterated that specific jurisdiction requires a “strong relationship among the defendant, the forum and the litigation” (Ford Motor Company v Montana Eighth Judicial District Court, 141 S Ct 1017 [2021]).

Subject Matter Jurisdiction

By contrast, subject matter jurisdiction is the power of the court to hear a given type of claim. In the antitrust context, as courts and litigants grapple with the practical realities of increasingly global supply chains and cross-border finance, this question is frequently considered in terms of the territorial limitations applied to the Sherman Act’s bar on conspiracies that restrain trade. The US Foreign Trade Antitrust Improvements Act of 1982 (FTAIA) limits the territorial reach of US antitrust law to domestic or import commerce, and places foreign or export conduct beyond the reach of US courts unless that conduct has a “direct, substantial and reasonably foreseeable effect” on US commerce and that effect “gives rise to” a US antitrust claim (15 USC Section 6a).

Whether the causal nexus between foreign conduct and domestic effect is sufficiently direct will depend on the facts and circumstances, including the structure of the market and the relationships of the parties. Appeals courts presently disagree on whether the FTAIA’s directness prong requires that the US effect follow as the “immediate consequence” of the foreign antitrust conduct or whether the domestic effect must only bear a “reasonably proximate causal nexus” to that conduct (compare United States v Hui Hsiung, 778 F 3d 738 [9th Cir 2015] [“immediate consequence”] with Lotes v Hon Hai Precision Industries, 753 F 3d 395 [2d Cir 2014] [“reasonably proximate causal nexus”]). Nevertheless, however the test is expressed, the appeals courts generally appear to agree that the wholly foreign price fixing and sale of components included in goods sold to US consumers can have a direct effect on US commerce.

The exchange of evidence between parties in federal antitrust litigation is governed by the general rules for discovery in federal court. Those rules contain a permissive standard for what evidence parties may request: “any non-privileged matter that is relevant to any party’s claim or defence”, whether or not that information would ultimately be admissible at trial (Fed R Civ P 26[b][1]). Parties may request production of documents and electronically stored information, written responses to questions and requests for admissions, as well as depositions of witnesses of fact or corporate representatives. Non-US litigants may, in some circumstances, need to provide disclosure that would not be permitted under their own country’s laws. In addition, litigants may serve subpoenas seeking discovery from non-litigants.

Under these standards, discovery in US federal litigation is, in general, more burdensome, expensive and time-consuming than in many other jurisdictions. In the antitrust context, discovery can be particularly costly because class actions and other antitrust cases usually raise a variety of complex issues. Some constraints on the scope of discovery do exist. Since 2015, the federal rules have limited permissible discovery to relevant information that is “proportional to the needs of the case” (Fed R Civ P 26[b][1]). Parties may resist discovery requests on a variety of grounds, including that the requested materials fail the relevance standard or that compliance would be unduly burdensome under the circumstances.

In addition, the Supreme Court – recognising that the burdens of antitrust discovery can push defendants to settle even weak cases – has instructed lower courts to take seriously their gatekeeping function at the motion-to-dismiss stage. In 2007, the Supreme Court clarified that, to survive a motion to dismiss an antitrust claim on the pleadings, plaintiffs must allege specific facts, which, if accepted as true, plausibly suggest and are not merely consistent with an antitrust violation (Bell Atlantic v Twombly, 550 US 544 [2007]). This decision has raised the bar on what plaintiffs must allege, often before a court will allow plaintiffs to request discovery from defendants.

The attorney-client privilege protects from the discovery process confidential communications between an attorney and client made for the primary purpose of seeking or providing legal advice. In the corporate setting, the attorney-client privilege extends to communications between attorneys and those employees who “will possess the information needed by the corporation’s lawyers” in order to provide sound legal advice, as well as to those employees who “will put into effect” that advice (Upjohn v United States, 449 US 383 [1981]). Importantly, in-house counsel communications may be protected by attorney-client privilege under US law. Furthermore, the privilege protects attorney-client communications made with a business purpose, so long as at least “one of the significant purposes” of the communication was obtaining or providing legal advice (see Kellogg Brown & Root, 756 F 3d 754 [DC Cir 2014]).

Internal corporate communications that do not include attorneys may sometimes remain subject to the privilege, including where those communications reflect an attorney’s legal advice or where a non-attorney – such as in a compliance or internal audit role – is gathering facts at the direction of an attorney for the purpose of facilitating the attorney’s provision of legal advice to the company.

Limitations (and Exceptions to Those Limitations) on the Scope of Privilege

There are some important limitations on the scope of the privilege protection. For example, only the substance of legal advice (or of a request for advice) is protected. The fact of an attorney-client communication is not protected, nor are pre-existing non-privileged materials protected simply because they are shared between an attorney and a client. In addition, a party generally waives privilege protection by failing to maintain the confidentiality of legal advice, including by sharing that advice with third parties. There is no exception to this waiver for voluntary disclosure of privileged communications to the government (though, importantly, the US antitrust authorities do not demand that an investigative target hand over privileged materials to be seen as co-operative in a government investigation). The privilege also does not protect attorney-client communications made for the purpose of committing or furthering a crime or fraud (United States v Zolin, 491 US 554 [1989]).

The “common interest” protection – an exception to the rule that sharing legal advice with third parties results in a privilege waiver – safeguards against the compelled disclosure of communications between parties and their respective counsel when aligned in a common legal interest. Federal appeals courts disagree as to whether the common interest protection is limited to communications between parties when threatened by litigation; a number of appeals courts recognise that the privilege applies to the “full range of communications otherwise protected by the attorney-client privilege” without regard to whether litigation is threatened (United States v BDO Seidman, 492 F 3d 806 [7th Cir 2007] [agreeing with at least five sister circuits that the threat of litigation is not required for the common interest protection to apply]; but see Santa Fe Int’l, 272 F 3d 705 [5th Cir 2001] [finding that the protection only applies where there is the threat of litigation]). In federal antitrust litigation, co-defendants regularly invoke the common interest protection to share materials and collaborate on defence strategy. Frequently, co-defendants will sign a joint defence agreement formalising that arrangement (but this step is not strictly required for the common interest protection to apply).

A related protection arises under the “work product” doctrine, which shields from disclosure materials “prepared in anticipation of litigation” (Fed R Civ P 26[b][3]). It protects both “documents and tangible things” and the “mental impressions, conclusions, opinions or legal theories of a party’s attorney”. The work product doctrine is not an absolute bar to compulsory disclosure of qualifying materials. Rather, an adversary may ask the court to compel disclosure of work product by showing that the requesting party has a “substantial need” for the materials in order to prepare its case and that the party cannot, without “undue hardship”, obtain through other means the “substantial equivalent” of the requested materials (Fed R Civ P 26[b][3][A]). In practical terms, however, this standard is very challenging to meet.

As described in 2.3 Impact of Competition Authorities, agreements to settle most forms of enforcement proceedings by the US federal antitrust authorities are typically made public in the course of a federal court’s review of the proposed resolution. One exception to this general rule is for parties who qualify for leniency pursuant to the Department of Justice, Antitrust Division’s Corporate Leniency Policy. The Leniency Program, a centrepiece of the Division’s criminal cartel enforcement efforts for more than 25 years, accords immunity from criminal antitrust prosecution to corporations that report their role in a per se antitrust violation at an early stage and meet certain other conditions, including co-operating fully with the Division’s prosecutions of co-conspirators and making restitution to injured parties.

To encourage applicants to come forward, the Division’s policy is to treat as confidential the identity of leniency applicants and the materials they provide. The Division acknowledges that it will disclose the identity of a leniency applicant if ordered to do so by a court, though such an order would be unusual. While at least one appeals court has held that the Division must disclose leniency agreements pursuant to requests under the US Freedom of Information Act (FOIA), that court also recognised that details within those materials identifying a leniency recipient could be exempt from FOIA disclosure (Stolt-Nielsen Transportation Group v United States, 534 F 3d 728 [DC Cir 2008]).

That said, a conditional leniency recipient will likely identify itself to plaintiffs in follow-on civil litigation, in an effort to fulfil its restitution obligation under the Leniency Policy by co-operating with plaintiffs and earning the resulting de-trebling of damages available under the Antitrust Criminal Penalty Enhancement and Reform Act of 2004 (ACPERA).

In addition, public companies may face other legal obligations, such as under the securities laws, to disclose their status as the recipient of leniency.

On 4 April 2022, the Division updated its Leniency Policy. This update imposed a number of more stringent obligations on leniency applicants while giving the Department of Justice more discretion as to when to award leniency. These additional obligations include:

• “prompt” reporting upon internal discovery of the activity;
• best efforts to remediate (in addition to providing restitution); and
• best efforts to improve compliance programmes to mitigate future risks.

Litigants in US federal court may rely on, and compel, testimony from fact witnesses both before and during trial. Prior to trial, the principal tool for compelling a witness to testify is a deposition, in which the requesting litigant compels the witness to attend an in-person interview to provide sworn testimony in front of a judicial officer. Parties can also request that opposing parties respond to written questions, called interrogatories. In either case, the court may compel the witness to respond under threat of sanction. During trial, judges generally prefer live testimony so that the fact-finder can evaluate the witness’s credibility and so that the opposing party can cross-examine the witness. Deposition testimony may be admitted into evidence to contradict or impeach testimony given during trial, or in some cases if a witness is unavailable to testify in court.

The rules governing federal court litigation, including antitrust claims, permit parties to rely on expert evidence both before and during trial. In the antitrust context, the parties nearly always rely on one or more experts to establish or challenge key issues, including:

• whether a purported class of plaintiffs satisfies the requirements for certification;
• the appropriate contours of the relevant product market;
• a party’s market power (or lack thereof); and
• the proper measure of damages.

Experts will generally prepare a written report (which must be provided to the opposing party prior to trial) and provide in-person testimony (Fed R Civ P 26[a][2]).

An expert’s testimony is admissible as evidence only if the court determines that:

• the expert’s specialised knowledge will assist the fact-finder;
• the testimony is based on sufficient facts or data;
• the testimony is the product of reliable principles and methods; and
• the expert has reliably applied these principles and methods to the facts of the case.

This assessment requires the court to scrutinise the expert’s particular methods and their degree of acceptance in the relevant field (see Daubert v Merrell Dow Pharmaceuticals, 509 US 579 [1993]; Fed R Evid 702). Before or during trial, parties can challenge the admissibility of opposing expert testimony or dispute the validity of that testimony. Parties may depose opposing experts, cross-examine them at trial, and seek to introduce evidence that purports to conflict with an expert’s conclusions.

The Clayton Act does not provide for punitive damages. Instead, plaintiffs who suffer antitrust injury may recover treble damages. For consumer plaintiffs injured by a price-fixing or a market-division cartel, common measures of damages include the amount of the overcharge caused by the conspiracy, measured by identifying the price they would have paid but for the restraint. For competitor plaintiffs injured by a monopolist’s exclusionary conduct, a common measure of damages is the plaintiff’s resulting lost profits.

As with the other elements of a civil antitrust action, plaintiffs must establish the value of their injury by a preponderance of the evidence standard. The Clayton Act permits damages assessments to be made “in the aggregate” according to “statistical or sampling methods” accepted by the court (15 USC Section 15d). In practice, antitrust plaintiffs nearly always rely on an expert to quantify damages according to an accepted model. Plaintiffs must also prove that the damages were not caused by separate and independent factors (ie, they are required to disaggregate the losses caused by the alleged antitrust violation).

As discussed in 2.5 Pass-On Defence, defendants in federal antitrust litigation cannot escape liability by establishing that direct purchasers passed on to indirect purchasers some or all of an anti-competitive overcharge (Hanover Shoe v United Shoe Mach, 392 US 481 [1968]).

A statutory exception to the treble damages rule exists for defendants who successfully receive leniency from prosecution under the Division’s Leniency Policy. Under the Antitrust Criminal Penalty Enhancement and Reform Act (ACPERA), leniency recipients who provide “satisfactory co-operation” to plaintiffs in follow-on civil litigation may have their damages limited to actual damages, rather than treble damages. Courts have not assessed with any precision what constitutes a defendant’s satisfactory co-operation, but defendants can expect that in order to receive what is known as ACPERA credit they will need to provide evidence to plaintiffs in support of their antitrust claims.

Section 4 of the Clayton Act enables plaintiffs to recover interest on damages awards. Pre-judgment interest awards are discretionary: a federal district court may award interest on actual damages – but not for the full treble damages available under the antitrust laws – for any period from the date of service of the plaintiff’s pleading to the date of judgment, when just in the circumstances. That standard considers whether defendants acted intentionally to delay resolution of the proceedings (15 USC Section 15[a]).

By contrast, post-judgment interest is mandatory: the court must award interest on a damages award until the defendant(s) transfers the funds to the plaintiff(s). The interest – at a rate equal to the weekly average one-year constant maturity Treasury yield for the calendar week preceding the date of the judgment – is calculated from the date of the entry of judgment and is compounded annually (28 USC Section 1961). Each state’s antitrust laws provide for post-judgment interest; the law on pre-judgment interest varies from state to state.

US antitrust law follows the common law tort principle of joint and several liability, which means that each defendant can be responsible for paying the entire damage award for the conspiracy as a whole (not just for damages to purchasers with whom a given defendant transacted).

However, as discussed in 6.3 Leniency and Settlement Agreements and 8.1 Damages: Assessment, Passing on and Interest, successful recipients of leniency from the Division’s antitrust prosecution who provide “satisfactory co-operation” to follow-on litigants may have their civil damages claim limited to actual damages under ACPERA. In addition, the leniency recipient will not be liable to plaintiffs on a joint and several basis for the harm from the entire conspiracy, but will instead be held liable only for its own harm to the plaintiffs.

The US Supreme Court has ruled that a defendant found jointly and severally liable under the federal antitrust laws for treble damages, costs and attorneys’ fees has no right to seek contribution from co-conspirators for their share of the damages award (Texas Industries v Radcliffe Materials, Inc, 451 US 630 [1981]). Rather, a single defendant may have to pay the entire damages award for three times the harm caused by the entire conspiracy. A court may subtract from the damages calculation any settlement that other defendants have paid to resolve the litigation, but those settlement amounts are likely to reflect a discount to the settling defendants.

This dynamic can pressure defendants to settle before trial by exposing non-settling defendants to the risk of bearing a disproportionate share of liability for their role in a multiparty conspiracy. Courts do not permit co-defendants to agree to indemnify each other for liability, but have generally upheld agreements between them to pay a proportionate share of any judgment based on, for example, each defendant’s market share.

The Clayton Act permits private plaintiffs to sue for injunctive relief against any “threatened loss or damage by a violation of the antitrust laws” (15 USC Section 26). To obtain injunctive relief, a plaintiff must show that:

• it has suffered irreparable injury that cannot be compensated for by other remedies, such as monetary damages;
• the balance of hardships between the plaintiff and defendant favour an injunction; and
• the injunction is in the public interest (eBay v MercExchange, 547 US 388 [2006]).

The Clayton Act also allows plaintiffs to seek interim relief – in the form of a preliminary injunction that can be obtained prior to trial – if the plaintiff is able to show a “likelihood of success on the merits” of its claim and meet other requirements (North American Soccer League v US Soccer Fed’n, 883 F 3d 32 [2d Cir 2018]). A preliminary injunction requires a hearing and notice to the opposing party (although in exceptional circumstances parties can seek a temporary restraining order without such notice or a hearing) (Fed R Civ P 65). The party seeking a preliminary injunction must post a security bond to compensate the opposing party if the injunction is found to have been unwarranted. Notably, the bar on damages claims by indirect purchasers under the federal antitrust laws does not extend to claims for injunctive relief.

Alternative dispute resolution is available in antitrust litigation on similar bases as it is in other federal court litigation. Federal judicial policy favours arbitration, as a matter of contract between parties. While courts cannot compel parties to arbitrate their disputes in the absence of an agreement between them to do so, courts will rigorously enforce arbitration agreements according to their terms. In recent years, the US Supreme Court has applied this principle to arbitration agreements in boilerplate consumer contracts, in ways that have important consequences for private antitrust litigants. The Court has held that parties may not be compelled to arbitrate on a class-wide basis, in the absence of an agreement to do so (Stolt-Nielsen v AnimalFeeds Int’l, 559 US 662 [2010]). A year later, the Court invalidated state laws seeking to bar enforcement of class arbitration waivers in consumer agreements (AT&T Mobility v Concepcion, 563 US 333 [2011]).

These rulings could make it more challenging for consumers to pursue class-wide recovery under the antitrust laws. Indeed, most recently, the Supreme Court affirmed – in the antitrust context – that contractual waiver of class arbitration is enforceable even if the cost of individually arbitrating exceeds a claimant’s potential for recovery (American Express v Italian Colors Restaurant, 570 US 228 [2013]).

Litigation funding is a developing industry in the USA and may be available to support civil litigation under the antitrust laws. However, opponents of litigation funding have challenged these arrangements as being illegal “champerty” – the practice of acquiring an interest in pursuing a third party’s cause of action in exchange for a portion of the proceeds if litigation succeeds. See, for example, Boling v Prospect Funding Holdings, 771 Fed Appx 562 (6th Cir 2019).

In 2024, the litigation finance industry experienced a continued contraction in new capital commitments, with a 16% year-over-year decline. New commitments are now nearly 30% below 2022 levels. The contraction is largely supply-driven, as funders face greater difficulty raising capital amidst broader challenging financial conditions.

Section 4 of the Clayton Act provides that plaintiffs “shall recover” the costs associated with successfully litigating their claim, including “a reasonable attorney’s fee” (15 USC Section 15[a]). Typically, plaintiff lawyers acting for a purported class work on contingency and seek to recover a percentage of any court-approved settlement or trial award. By contrast, defendants have no general statutory right to recover their costs of successfully defending a federal antitrust litigation. The lone means of recovering defence costs is for the court to impose monetary sanctions on plaintiffs under the federal rules – for example, based on a finding that plaintiffs (or their attorneys) have asserted frivolous claims or arguments (Fed R Civ P 11).

Sanctions – particularly significant monetary penalties – are exceedingly rare and an unreliable source of recovery of defence costs. The unavailability of defence costs to serve as a headwind on speculative antitrust claims is one reason the courts take seriously their gatekeeper role in assessing defendants’ threshold challenges to the sufficiency of an antitrust complaint.

Typically, courts will not order a litigant to post security for its opponent’s litigation costs. The exception is that parties seeking preliminary injunctive relief must provide a security in an amount sufficient to pay the costs and damages sustained if the party is found to have been wrongfully enjoined or restrained (Fed R Civ P 65).

A litigant adversely affected by a decision of a federal district court may seek to appeal that decision to an intermediate federal court of appeals. Parties may generally appeal a lower court’s conclusions of law according to a de novo standard, under which the appeals court will analyse the legal question without deferring to the district court’s analysis. While an appellant may also challenge a lower court’s factual findings, the appeals court will apply a far more deferential standard of review, generally leaving fact conclusions undisturbed unless clearly erroneous.

Whether, and when, a party may challenge a district court decision can take on great significance, particularly in complex litigation such as an antitrust class action. A party generally has the right to appeal “final decisions of the district courts” (28 USC Section 1291). A decision is “final” if it “ends the litigation on the merits” (Catlin v United States, 324 US 229 [1945]). The policy of the “final judgment rule” is intended to promote efficiency and limit delay, by seeking to ensure that, where possible, all challenges to lower-court decisions are resolved in a single appeal.

By contrast, only in limited circumstances will courts permit appeals of interlocutory orders that do not finally resolve the dispute. In general, interlocutory appeals are reserved for “controlling questions of law” about which there is “substantial ground for difference of opinion” and resolution of which would “materially advance the ultimate termination of the litigation” (28 USC Section 1292[b]). The federal rules authorise – but do not require – interlocutory appeal of a decision on class certification (Fed R Civ P 23[f]). Parties who lose on appeal may petition the US Supreme Court for final review of the appellate decision. Supreme Court review is discretionary, and as a practical matter is rarely granted.

Algorithmic Pricing

Legislators’ concern continues over potential misuse of artificial intelligence and algorithmic pricing to reduce competition. Nearly half of state legislatures across the USA are contemplating legislation restricting algorithmic pricing, proposing to prevent companies from using algorithms to collude to set higher prices. Connecticut and New York are the first and second states, respectively, to pass their bills into law.

Additionally, US agencies are focused on the potential for algorithmic pricing to lead to price fixing and have withdrawn long-established safety zones that provided guidance on when competitors could share pricing and salary information. Ongoing cases concerning algorithmic collusion include the Department of Justice’s litigation against RealPage, which allegedly co-ordinated higher prices among lessors of accommodations by collecting their competitively sensitive information and feeding it into an algorithm, and recommending prices based on the output. Additionally, in an ongoing case, the Department of Justice alleged that Agri Stats, a data company in the meat-processing industry, operated an information-sharing scheme that allowed competitors to exchange vast quantities of competitively important data.

Mobile Application Stores

The Open App Markets Act was reintroduced in June 2025 by US senators, led by Marsha Blackburn (Republican-Tennessee) and Richard Blumenthal (Democrat-Connecticut), along with Amy Klobuchar (Democrat-Minnesota), Dick Durbin (Democrat-Illinois) and Mike Lee (Republican-Utah). This bill targets Apple’s App Store and Google’s Play Store. The bill would require app store providers to allow third-party app stores, permit application “sideloading” (which allows customers to install apps on a device from sources other than the official app store) and enable alternative in-app payment systems, while banning app store operators from self-preferencing their own apps in search results. These measures aim to open up the mobile application marketplace to more competition and give both developers and consumers more choices. The original bill passed a Senate committee in 2022 but never made it to the full vote. Its reintroduction in 2025, backed by both Republicans and Democrats, signals ongoing bipartisan support for targeting big tech application distribution.

Growth in Antitrust Class Actions

The USA continues to represent the most mature and developed market for antitrust class actions. In 2025–2026, the spotlight on antitrust class actions is expected to continue, focusing particularly on big tech. Landmark cases against Google, Apple and Meta are set to test the limits of antitrust laws in the digital realm and the remedies that courts should impose for antitrust violations. Aggressive government enforcement continues, helping to fuel continued private class actions addressing similar issues.

Growth in State Pre-Merger Notifications

More states have been passing pre-merger notification laws that allow state attorneys general to review mergers alongside federal antitrust agencies. Washington’s and Colorado’s new notification law are effective as of summer 2025. California will implement notification requirements for parties filing on or after 1 January 2026. Similar legislation in the District of Columbia, Hawaii, New York and West Virginia is also being considered. This legislation will allow states to gain access to transaction information earlier or simultaneously with federal antitrust agencies, initiate investigations or requests proactively, and co-ordinate or act independently of the federal antitrust agencies. State notification of proposed transactions could potentially increase litigation risk for merging parties, especially if they fail to comply with state requirements.