Formed in 1939 to protect the interests of general aviation pilots and private aircraft owners, the Aircraft Owners and Pilots Association (AOPA) grew to be the world's largest civil aviation organization during the twentieth century. As of 2020, AOPA's mission statement was the following : "We protect your freedom to fly by advocating on behalf of our members; educating pilots, nonpilots, and policy makers alike; supporting activities that ensure the long-term health of General Aviation; fighting to keep General Aviation accessible to all; and securing sufficient resources to ensure our success."

Under first executive director Joseph B. "Doc" Hartranft's (1915-2002) leadership, AOPA lobbied for the establishment of the Civilian Pilot Training Program. During the Second World War, AOPA formed the AOPA Air Guard and worked with the Air Force and Navy to train pilots for military service and for work with the Office of Strategic Services (OSS). After the war the organization resumed its lobbying activities, opposing the efforts of the commercial airlines to restrict access to major airports. The AOPA also opposed congressional and state efforts to regulate general aviation and to set standards for mandatory safety equipment and radar devices for private aircraft. The organization worked closely with the manufacturers of small planes, particularly Piper and Beechcraft, in order to develop and test aircraft. It also provided private health and life insurance for its members, who often could not get coverage from commercial carriers.

Protecting local airports from closure threats was a priority in the 1990s and continued into the next decades. In 1994, AOPA successfully lobbied for the passage of product liability reform legislation. The organization also supported the Aviation Investment and Reform Act (AIR-21), which passed in 2000 and allocated funds for airport and airway modernization. AOPA continued to operate for the interests of civilian aircraft owners and pilots after the September 11 Terrorist Attacks. In subsequent years, AOPO has advocated against general aviation user fees and has launched multiple programs to encourage flying clubs and to improve the flight training experience for students.