American antitrust laws are state and federal laws created to prevent monopolies. Antitrust laws apply to both businesses and individuals. The philosophy behind the laws is that trusts and monopolies can stagnate markets and prevent others from engaging in healthy market competition.

All American antitrust laws date back to the Sherman Antitrust Act of 1890 that was passed by Congress to remove limits on competitive trade. The Sherman Antitrust Act affects all interstate business transactions. Section 1 of the Sherman Act states that the courts are to interpret which contracts unfairly restrict trade. Section 2 deems it illegal for a company or an individual "to monopolize, or attempt to monopolize."

Courts usually decide on antitrust cases on the grounds that a monopoly itself may be justified only if justifiable business practices warrant it. We can think about the example of a manufacturing company that has to produce and use its own parts in a product to ensure consumer safety standards are met. Competition is being limited by the company, but if public safety is at risk, the courts would probably rule that antitrust laws have not been violated as the motive is consumer safety and not one of purposefully limiting competition.

The Federal Trade Commission (FTC)is legally permitted to interpret and enforce section 5 of the Federal Trade Commission Act's antitrust laws. Section 5 discusses "unfair methods of competition" but does not define what the "unfair methods" are in relation to trade restrictions. The FTC must enforce the standards and interpret the law in each particular antitrust case.

Another antitrust law, The Clayton Act, covers mergers and acquisitions. No merger or acquisition is permitted if the result of doing so "may be substantially to lessen competition, or to tend to create a monopoly." Again, the antitrust law is open to interpretation on a case by case basis, which sometimes necessitates the evidence of comprehensive economic market studies.