The Amateur Athletic Union (AAU) is an amateur sports organization based in the United States. A multi-sport organization, the AAU is dedicated exclusively to the promotion and development of amateur sports and physical fitness programs. It has more than 700,000 members nationwide, including more than 100,000 volunteers. The philosophy of the AAU is "Sports for All, Forever."

Amateur sports are sports in which participants engage largely or entirely without remuneration. The distinction is made between amateur sporting participants and professional sporting participants, who are paid for the time they spend competing and training. In the majority of sports which feature professional players, the professionals will participate at a higher standard of play than amateur competitors, as they can train full-time without the stress of having another job. The majority of worldwide sporting participants are amateurs.