The Clayton Antitrust Act of 1915, (October 151914, ch. 323, , codified at , ), was enacted in the United States to add further substance to the U.S.antitrust law regime. That regime started with the Sherman Antitrust Act of 1890, the first Federal law outlawing practices considered harmful to consumers (monopolies and cartels). The Clayton act specified particular prohibited conduct, the three-level enforcement scheme, exemptions, and remedial measures.

Passed during the Wilson administration, the legislation was first introduced by Alabama Democrat Henry De Lamar Clayton in the U.S. House of Representatives, where the act passed by a vote of 277 to 54 on June 5th, 1914. Though the Senate passed its own version on September 2nd, 1914 by a vote of 46-16, the final version of the law (written after deliberation between Senate and the House), did not pass the Senate until October 5th and the House until October 8th of the same year.

Like the Sherman Act, much of the substance of the Clayton Act has been developed and animated by the U.S. courts, particularly the Supreme Court.