The Treaty on Open Skies was signed on 24 March 1992 by 27 members of NATO and the former Warsaw Pact; it entered into force as a legally binding document on 1 January 2002. In the following years, the number of States Parties increased to 34 as a result of further accessions.
The Treaty gives each State Party the right to conduct a certain number of agreed observation flights a year over the territory of other States Parties. Sensors for photo and video images are used during these flights, along with more and more digital sensors.
Because representatives of both the observing and the observed states participate in all observation flights, the Treaty plays an important role in creating transparency and building confidence. Observation flights can also be used to obtain a picture of the situation in international crises and to monitor the environment.
To date, over 1,500 observation flights have been conducted under the Open Skies regime. Germany has been involved in more than 12% of these flights. The Open Skies Consultative Commission (OSCC), which is based in Vienna and maintains several informal working groups, is the primary consulting and decision-making body for issues related to implementing and further developing the Treaty on Open Skies. At the national level in Germany, the Federal Armed Forces Verification Centre is responsible for coordinating, processing and assessing the images that are collected during all observation flights involving Germany.
In November 2020, the United States became the first State Party to withdraw from the Treaty. In June 2021, Russia also declared its withdrawal from the Treaty. Its withdrawal will become legally binding after six months.