Antitrust law, any law restricting business practices considered unfair or monopolistic. The United States has the longest standing policy of maintaining competition among business enterprises through a variety of laws. The best known is the Sherman Antitrust Act of 1890, which declared illegal “every contract, combination . . . or conspiracy in restraint of trade or commerce.” Another important U.S. antitrust law, the Clayton Antitrust Act of 1914, as amended in 1936 by the Robinson–Patman Act, prohibits discrimination among customers through prices or other means; it also prohibits me...