The American Theatre Organ Society (ATOS) is an international non-profit organization comprised of worldwide volunteer members who are committed to helping preserve and perpetuate the musical theatre pipe organ heritage that began in the early 20th century. Membership is made up of musicians, technicians, hobbyists, educators, and others who enjoy the music of the theatre pipe organ. Founded in 1955, the ATOS consists of regional member-chapters and is led by democratically elected leaders. It operates in accordance with 501 (c) (3) regulations.