In simple terms
Antitrust law sets limits on how companies may compete. It targets conduct that protects a firm’s position by shutting rivals out, rather than by serving customers better.
Outside the United States the same field is usually called competition law. The names differ; the core concerns are close.
How it works
Enforcement runs along three tracks.
- Agreements between firms. US law bars agreements that unreasonably restrain competition. EU law prohibits agreements between independent market operators that restrict competition. The gravest form is a cartel, where competitors secretly fix prices or carve up markets.
- Abuse of market power. US law makes it illegal to monopolize or attempt to monopolize. EU law bars a dominant firm from abusing that position, for instance through unfair pricing or by limiting production.
- Mergers. A deal can be blocked where its effect may be substantially to lessen competition or tend to create a monopoly.
Courts sort conduct by how clearly harmful it is. Some practices, such as price fixing and bid rigging, are treated as illegal in themselves, with no inquiry into their actual market effects. Others are judged under a rule of reason, weighing intent and consequences together.
Who enforces it varies. In the United States it is mainly the Federal Trade Commission and the Department of Justice. In the European Union it is the European Commission, working alongside national authorities.
Why it matters
Antitrust decides whether a market stays open to newcomers, which shapes prices, choice and where innovation can happen.
It is also where the largest technology deals are tested, because concentrated control of key infrastructure is exactly what these rules were written to examine.
Where you’ll see it
- Regulators reviewing a large merger or licensing deal.
- Cartel investigations and the fines that follow.
- Court cases over whether a dominant firm abused its position.
Example
Competitors who secretly agree to charge the same price are operating a cartel, the conduct both US and EU rules treat most seriously.
Often confused with
Consumer protection law. That governs how a firm treats its own customers, such as misleading advertising. Antitrust governs how a firm affects competition in a market.
Key facts
- Sherman Act section 1 prohibits agreements that unreasonably restrain competition; section 2 makes it illegal to monopolize or attempt to monopolize.1
- The Clayton Act bars mergers where the effect may be substantially to lessen competition or to tend to create a monopoly.1
- US antitrust law is enforced mainly by the Federal Trade Commission and the Department of Justice, which review mergers.1
- Price fixing, bid rigging and certain horizontal agreements are treated as illegal per se, without inquiry into actual market effects; other conduct is judged under the rule of reason established in Standard Oil v. US.1
- In the EU, Article 101 TFEU prohibits agreements between two or more independent market operators that restrict competition, and Article 102 prohibits firms holding a dominant position from abusing it.2
- The European Commission describes cartels, which may involve price fixing and market division among competitors, as the most serious violation of Article 101.2
This entry explains a legal term. Laws differ by country and change over time. It is not legal advice.
Go deeperHow Do Regulators Decide a Company Is Too Powerful?Related concepts
In the news
Quick checkWhat is the difference between a per se violation and one judged under the rule of reason?Show answer
A per se violation is illegal in itself, with no inquiry into market effects. The rule of reason weighs intent and actual consequences.
Sources
- Cornell Law School, Legal Information Institute. Antitrust laws (Wex). Last reviewed October 2024 (accessed 14 September 2026)
- European Commission, Directorate-General for Competition. Antitrust and cartels. Undated (accessed 14 September 2026)
Editorially reviewed by Specialty Digest Editorial TeamLast reviewed September 17, 2026Researched and drafted with AI assistanceReport an issue