A fixed-base operator (FBO) is an organization granted the right by an airport to operate at the airport and provide aeronautical services such as fueling, hangaring, tie-down and parking, aircraft rental, aircraft maintenance, flight instruction, and similar services. In common practice, an FBO is the primary provider of support services to general aviation operators at a public-use airport and is on land leased from the airport, or, in rare cases, adjacent property as a "through the fence operation". In many smaller airports serving general aviation in remote or modest communities, the town itself may provide fuel services and operate a basic FBO facility. Most FBOs doing business at airports of high to moderate traffic volume are non-governmental organizations, either privately or publicly held companies.

Though the term fixed-base operator originated in the United States, the term has become more common in the international aviation industry as business and corporate aviation has grown. The term has not been officially defined as an international standard, but there have been recent uses of the term in International Civil Aviation Organization (ICAO) publications such as Implementing the Global Aviation Safety Roadmap.