"The United States, Canada, and 22 European nations signed the Treaty on Open Skies on March 24, 1992. The treaty entered into force on January 1, 2002, and now has 34 member states. Each participant must permit unarmed observation aircraft to fly over its entire territory to observe military forces and activities. The treaty is designed to increase transparency, build confidence, reduce the chances of military confrontation, and encourage cooperation among the nations of Europe. According to the U.S. State Department, the parties have conducted more than 1,200 observation flights since the treaty entered into force. Nevertheless, the State Department has indicated that Russia is violating some treaty obligations. In addition, some Pentagon officials have questioned Russia's plan to upgrade cameras and sensors on the aircraft it employs for U.S. overflights." The report goes on to discuss key provisions of the Open Skies Treaty, as well as Russian compliance.
CRS Insight, IN10502
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html