What is United States Antitrust Law?

Legal Definition
United States antitrust law is a collection of federal and state government laws that regulates the conduct and organization of business corporations, generally to promote fair competition for the benefit of consumers. (The concept is called competition law in other English-speaking countries.) The main statutes are the Sherman Act 1890, the Clayton Act 1914 and the Federal Trade Commission Act 1914. These Acts, first, restrict the formation of cartels and prohibit other collusive practices regarded as being in restraint of trade. Second, they restrict the mergers and acquisitions of organizations that could substantially lessen competition. Third, they prohibit the creation of a monopoly and the abuse of monopoly power.

The Federal Trade Commission, the U.S. Department of Justice, state governments and private parties who are sufficiently affected may all bring actions in the courts to enforce the antitrust laws. The scope of antitrust laws, and the degree to which they should interfere in an enterprise's freedom to conduct business, or to protect smaller businesses, communities and consumers, are strongly debated. One view, mostly closely associated with the "Chicago School of economics" suggests that antitrust laws should focus solely on the benefits to consumers and overall efficiency, while a broad range of legal and economic theory sees the role of antitrust laws as also controlling economic power in the public interest.
-- Wikipedia