The American Federation of Labor was a national federation of labor unions in the United States that continues today as the AFL–CIO. It was founded in Columbus, Ohio, in 1886 by an alliance of craft unions eager to provide mutual support and disappointed in the Knights of Labor. Samuel Gompers was elected the full-time president at its founding convention and was re-elected every year except one until his death in 1924. He became the major spokesperson for the union movement.

Labor unions represent United States workers in many industries recognized under US labor law since the 1935 enactment of the National Labor Relations Act. Their activity today centers on collective bargaining over wages, benefits, and working conditions for their membership, and on representing their members in disputes with management over violations of contract provisions. Larger labor unions also typically engage in lobbying activities and electioneering at the state and federal level.