The Treaty on Open Skies establishes a program of unarmed aerial surveillance flights over the entire territory of its participants. The treaty is designed to enhance mutual understanding and confidence by giving all participants, regardless of size, a direct role in gathering information about military forces and activities of concern to them. It entered into force on 1 January 2002, and currently has 34 party states. The idea of allowing countries to openly surveil each other is thought to prevent misunderstandings and limit the escalation of tensions. It also provides mutual accountability for countries to follow through on treaty promises.

Surveillance aircraft are aircraft used for surveillance. They are primarily operated by military forces and government agencies in roles including intelligence gathering, maritime patrol, battlefield and airspace surveillance, observation, and law enforcement.