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 located either on airport leasehold property or, in rare cases, adjacent to airport leasehold 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, i.e., either privately or publicly held companies.
Though the term fixed-base operator originated in the United States, the term is becoming more common in the international aviation industry as business and corporate aviation grows. 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. 
After the end of World War I in November 1918, civil aviation in the United States was primarily unregulated and was primarily made up of " barnstormers," who were transient pilots flying inexpensive military surplus aircraft from city to city, often landing in farm fields on the outskirts of a town because airports were scarce at that time. These traveling aviators offered airplane rides and aerobatic flight demonstrations, and they frequently collaborated as "flying circuses" and performed impromptu airshows for the townsfolk, charging whatever the local economic conditions would allow. As a result, mechanics and early flight instructors moved around with the aircraft and had no established business in any one location.
With passage of the Air Commerce Act of 1926 and its resulting requirements for the licensing of pilots, aircraft maintenance requirements, and regulations in training standards, the transient nature of civil aviation was curtailed. The pilots and mechanics who made their living on the road began establishing permanent businesses, termed fixed-base operations, at the growing number of airports appearing throughout the United States as a way to distinguish permanent businesses from the transient businesses common prior to 1926. 
Fixed-base operators support a wide range of aeronautical activities which may include one or more of the following:
- Sale of aviation fuel – piston aircraft fuel ( avgas) and/or turbine aircraft fuel ( Jet-A or Jet A-1)
- Line services for general aviation aircraft
- Air taxi and air charter operations
- Scheduled or nonscheduled air carrier services and support services
- Pilot training
- Aircraft rental and sightseeing
- Aircraft sales and service
- Aircraft storage (tie-down or hangar)
- Repair and Aircraft maintenance.
- Sale of aircraft parts
- Aerial photography
- Crop dusting and aerial applications
- Aerial advertising and Aerial survey
Though not required, fixed-base operators generally also provide at least basic auxiliary services to pilots, flight crew, and passengers such as restroom facilities, telecommunication services, and waiting areas. General aviation FBOs (commonly in the U.S.) sometimes provide Courtesy Cars that can be used for free or little cost by flight crews mostly for short trip from the airport and the surrounding city area. Larger and better equipped FBOs may additionally offer food vending and restaurant facilities, ground transportation arrangements taxi/limousine, shuttle van, flight planning and weather information areas (computer- or telephone-based), rest lounges and showers, aviation supplies shop (selling navigation charts, manuals, or in-flight comfort items), access to in-flight catering, and accommodations reservations or concierge services for both crew and passengers through a customer service representative (CSR).
At medium and large airports, FBOs are typically affiliated with one of the major aviation fuel suppliers and display the fuel supplier's sign prominently. At smaller airports, the FBO is often the airport operator or a flying club.
Within the United States, the Federal Aviation Administration (FAA) regulates some activities that may comprise an FBO such as the authorization or repair stations, flight training, and air taxi/air carrier services, but the overarching term "FBO" has no regulatory standards through the federal government. That said, the FAA has defined an FBO as "a commercial entity providing aeronautical services such as fueling, maintenance, storage, ground and flight instruction, etc., to the public." 
The United States Department of Transportation, in cooperation with the FAA, has the duty of establishing minimum standards for commercial aeronautical activities and recommends implementation of these standards by the airport operator or agency, commonly referred to as the airport sponsor.  The United States FBO Industry is represented nationally by the National Air Transportation Association or NATA, but is also partly represented by both the National Business Aviation Association (NBAA) and the Aircraft Owners and Pilots Association (AOPA).
The number of U.S. businesses meeting the minimum criteria as an FBO is 3,138 as of April 2009 according to a survey conducted by Aviation Resource Group International (ARGI). The number has decreased since the 2006 survey, which counted 3,346 FBOs. 
FBOs are taking some time to grow in the Asian continent, but they have appeared most notably in Hong Kong, Macau, Singapore, Kuala Lumpur, Shanghai and the Philippines. This is mainly due to the immaturity of the private and corporate aviation sector in Asia where there still exist very few of these aircraft when compared to the United States and Europe. However several companies do offer "FBO services" at airports throughout the region, making use of existing facilities, the main point being the provision of credit for overseas operators.
- U.S. Department of Transportation, Federal Aviation Administration, "Advisory Circular 150/5190-7: Minimum Standards for Commercial Aeronautical Activities", 28 August 2006, p. 13.
- U.S. Department of Transportation, Federal Aviation Administration, "Advisory Circular 150/5190-7: Minimum Standards for Commercial Aeronautical Activities", 28 August 2006, p. 14.
- International Civil Aviation Organization, "Implementing the Global Aviation Safety Roadmap", 28 August 2008, p. A-1.
- Air transportation: a management perspective, J. G. Wensveen, 2007, p. 67
- "FAA Airport Compliance Manual – Order 5190.6B" (PDF). www.faa.gov. Federal Aviation Administration.
- U.S. Department of Transportation, Federal Aviation Administration, "Advisory Circular 150/5190-7: Minimum Standards for Commercial Aeronautical Activities", 28 August 2006, p. 3.
- General Aviation in the United States: A Fact Book on General Aviation and Aviation Service Businesses Archived 2009-12-29 at the Wayback Machine. National Air Transportation Association, 2009, p. 10