The Treaty on Open Skies entered into force on January 1, 2002, and currently has 34 States Parties. It 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. Open Skies is one of the most wide-ranging international efforts to date promoting openness and transparency of military forces and activities. The concept of "mutual aerial observation" was initially proposed to Soviet Premier Bulganin at the Geneva Conference of 1955 by President Eisenhower; however, the Soviets promptly rejected the concept and it lay dormant for several years. The treaty was eventually signed as an initiative of President (and former Director of Central Intelligence) George H. W. Bush in 1989. Negotiated by the then-members of NATO and the Warsaw Pact, the agreement was signed in Helsinki, Finland, on March 24, 1992. The United States ratified it in 1993.

This treaty is not related to civil-aviation open skies agreements.