Treaty on Open Skies

Helsinki, Finland – 24 March 1992 (signature); 1 January 2002 (entry into force)

Open Skies established a regime of observation flights to enhance mutual understanding and confidence. Flights collect imagery and sensor data shared among parties under agreed quotas and procedures. The US withdrawal (2020) and Russia’s withdrawal (2021) curtailed the regime’s coverage.

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Key Features

• Quota system of observation flights; use of certified sensors.
• Short‑notice overflights of entire territory of States Parties.
• Joint missions and data sharing to increase transparency.

Source

• Official Treaty Text via United Nations Treaty Collection; background via OSCE and Arms Control Association.