The Sherman Antitrust Act (26 Stat. 209, 15 U.S.C. §§ 1–7) is a United States antitrust law which prescribes the rule of free competition among those engaged in commerce and consequently prohibits unfair monopolies. It was passed by Congress in 1890 and is named for Senator John Sherman, its principal author.
The Sherman Act broadly prohibits 1) anticompetitive agreements and 2) unilateral conduct that monopolizes or attempts to monopolize the relevant market. The Act authorizes the Department of Justice to bring suits to enjoin (i.e., prohibit) conduct violating the Act, and additionally authorizes private parties injured by conduct violating the Act to bring suits for treble damages (i.e. three times as much money in damages as the violation cost them).