Antitrust is the body of law, regulation and enforcement that protects competition in markets. It prohibits agreements between competitors to fix prices or share markets, stops dominant firms from using their power to exclude rivals, and reviews mergers that could substantially reduce competition. Its aim is to keep prices, quality, choice and innovation close to what open markets would deliver.
The term is American and comes from the "trusts" of the late 19th century, legal structures through which owners pooled control of competing companies, such as the Standard Oil Trust formed in 1882. Elsewhere the same field is usually called competition law. It works alongside, but is distinct from, sector regulation, consumer protection and financial regulation.
Antitrust in plain terms
Think of antitrust as the referee of the market. Businesses are allowed, and expected, to try to beat their rivals with better products and lower prices. What they are not allowed to do is rig the game: secretly agree with rivals not to compete, buy up every challenger before it can grow, or use their size to shut competitors out of shops, apps or supply chains.
When the referee spots a foul, it can fine the company, order it to stop, block a takeover, or in rare cases break a business into pieces. Customers rarely see the referee at work, but its rules shape the prices they pay and the choices they have.
The main antitrust laws
In the United States the core statutes are:
- The Sherman Act (1890). Section 1 bans contracts and conspiracies in restraint of trade, including cartels; Section 2 bans monopolization and attempts to monopolize.
- The Clayton Act (1914). It covers mergers and acquisitions that may substantially lessen competition, some forms of price discrimination and tying, and interlocking directorships, and lets injured parties sue for three times their damages.
- The Federal Trade Commission Act (1914). It created the Federal Trade Commission (FTC) and bans unfair methods of competition.
- The Hart–Scott–Rodino Act (1976). It requires large deals to be notified to the authorities before they close.
In the European Union, Article 101 of the Treaty on the Functioning of the European Union prohibits anti-competitive agreements and Article 102 prohibits abuse of a dominant position; the EU Merger Regulation (2004) governs mergers, and the Digital Markets Act (2022) sets obligations for large online "gatekeepers". The United Kingdom relies on the Competition Act 1998, the Enterprise Act 2002 and the Digital Markets, Competition and Consumers Act 2024. India enforces the Competition Act 2002 and Pakistan the Competition Act 2010.
Who enforces it
US enforcement is shared by the Department of Justice Antitrust Division, which can bring criminal cases, the FTC, state attorneys general and private plaintiffs. The European Commission's Directorate-General for Competition enforces EU rules alongside national authorities; the UK has the Competition and Markets Authority (CMA); India has the Competition Commission of India; and Pakistan has the Competition Commission of Pakistan. Large cross-border mergers are often reviewed by several authorities at once, which cooperate through the International Competition Network and the OECD.
What antitrust targets
- Cartels. Price fixing, bid rigging and market sharing are treated most severely, often as crimes, and most authorities offer leniency to the first participant to confess.
- Abuse of dominance or monopolization. A monopoly is not illegal in itself; using it to exclude rivals through exclusive contracts, predatory pricing, tying or refusal to deal can be.
- Mergers. Authorities assess whether a deal would raise prices or reduce innovation, often starting with market shares and the Herfindahl–Hirschman Index. Deals that turn an oligopoly into a duopoly attract close review.
- Buyer power. Wage-fixing and no-poach agreements among employers, which strengthen monopsony, are increasingly prosecuted.
Landmark cases include the break-up of Standard Oil (1911), the settlement that split up AT&T in 1984, and the Microsoft case decided on appeal in 2001. In August 2024 a US federal court ruled that Google had illegally maintained a monopoly in general search, and in April 2025 another found that it had monopolized parts of the advertising technology market. In November 2025 a federal judge ruled against the FTC in its case seeking to unwind Meta's purchases of Instagram and WhatsApp. In April 2025 the European Commission issued its first fines under the Digital Markets Act, €500 million against Apple and €200 million against Meta. In payments, the Department of Justice sued Visa in September 2024 over debit networks, and long-running litigation over card interchange fees has shaped the economics of card networks.
Schools of thought and debate
From the late 1970s, US antitrust was shaped by the consumer welfare standard associated with the Chicago school and Robert Bork's book The Antitrust Paradox (1978). It holds that the test of a business practice is its effect on consumers, mainly through prices and output, and that large size often reflects efficiency, including economies of scale.
The "neo-Brandeisian" movement, named after the US Supreme Court justice Louis Brandeis, argues that this standard has allowed excessive concentration, especially among digital platform companies that offer free services but gain lasting control through network effects. Its supporters want more attention to market structure, workers, suppliers and political power. Critics of that approach warn that vague goals make enforcement unpredictable and could penalize successful firms or protect competitors rather than competition. A further debate concerns regulatory capture and whether ex-ante rules for digital markets, such as the EU's Digital Markets Act, work better than case-by-case enforcement.