"...the Arms Control Association [does] so much to keep the focus on the issues so important to everyone here, to hold our leaders accountable to inspire creative thinking and to press for change. So we are grateful for your leadership and for the unyielding dedication to global nuclear security."

– Lord Des Browne
Vice Chairman, Nuclear Threat Initiative
October 20, 2014
The Open Skies Treaty at a Glance

Last Reviewed: 
November 2020

Contacts: Daryl Kimball, Executive Director, (202) 463-8270 x107

Signed March 24, 1992, the Open Skies Treaty permits each state-party to conduct short-notice, unarmed, reconnaissance flights over the others' entire territories to collect data on military forces and activities. Observation aircraft used to fly the missions must be equipped with sensors that enable the observing party to identify significant military equipment, such as artillery, fighter aircraft, and armored combat vehicles. Though satellites can provide the same, and even more detailed, information, not all of the treaty states-parties have such capabilities.  The treaty is also aimed at building confidence and familiarity among states-parties through their participation in the overflights.

President Dwight Eisenhower first proposed that the United States and the Soviet Union allow aerial reconnaissance flights over each other's territory in July 1955. Claiming the initiative would be used for extensive spying, Moscow rejected Eisenhower's proposal. President George H.W. Bush revived the idea in May 1989 and negotiations between NATO and the Warsaw Pact started in February 1990.

Treaty Status: The Open Skies Treaty entered into force on January 1, 2002, and 34 states are party to the treaty, though the Trump administration withdrew the United States from the treaty in November 2020.1

Twenty-six of the treaty’s initial 27 signatories have ratified the accord and are now states-parties. Since the treaty entered into force, Bosnia and Herzegovina, Croatia, Estonia, Finland, Latvia, Lithuania, Slovenia, and Sweden have become states-parties.

Territory: All of a state-party's territory can be overflown. No territory can be declared off-limits by the host nation.

Flight Quotas: Every state-party is obligated to accept a certain number of overflights each year, referred to as its passive quota, which is loosely determined by its geographic size.2 A state-party's active quota is the number of flights it may conduct over other states-parties. Each state-party has a right to conduct an equal number of flights over any other state-party that overflies it. A state-party's active quota cannot exceed its passive quota, and a single state-party cannot request more than half of another state-party's passive quota.

The treaty allows for multiple states-parties to take part in an overflight. The flight will count as an active flight for each state-party participating. Regardless of the number of observing states-parties, however, the overflight will only count as one passive overflight for the observed state-party.

Russia conducted the first observation flight under the treaty in August 2002, while the United States carried out its first official flight in December 2002. In 2008, states-parties celebrated the 500th overflight. Between 2002 and 2019, more than 1,500 flights have taken place.

Process: An observing state-party must provide at least 72 hours' advance notice before arriving in the host country to conduct an overflight. The host country has 24 hours to acknowledge the request and to inform the observing party if it may use its own observation plane or if it must use a plane supplied by the host. At least 24 hours before the start of the flight, the observing party will supply its flight plan, which the host has four hours to review. The host may only request changes in flight plans for flight safety or logistical reasons. If it does so, the two states-parties have a total of eight hours after submission of the original flight plan to agree on changes, if they fail, the flight can be cancelled. The observation mission must be completed within 96 hours of the observing party's arrival unless otherwise agreed.3

Although state-parties are allowed to overfly all of a member’s territory, the treaty determines specific points of entry and exit and refueling airfields. The treaty also establishes ground resolution thresholds for the onboard still and video cameras. The aircraft and its sensors must undergo a certification procedure before being allowed to be used for Open Skies in order to confirm that they do not exceed the allowed resolutions.

Aircraft: The treaty lays out standards for aircraft used for observation flights. Aircraft may be equipped with four types of sensors: optical panoramic and framing cameras, video cameras with real-time display, infra-red line-scanning devices, and sideways-looking synthetic aperture radar. For the first three full years after the treaty entered into force, the observation aircraft had to be equipped with at least a single panoramic camera or a pair of optical framing cameras. The states-parties may now agree on outfitting the observation planes with additional sensors.

Data: A copy of all data collected will be supplied to the host country. All states-parties will receive a mission report and have the option of purchasing the data collected by the observing state-party.

Treaty Implementation: The Open Skies Consultative Commission (OSCC), comprised of representatives of all states-parties, is responsible for the implementation of the Open Skies Treaty. The OSCC considers matters of treaty compliance, decides on treaty membership, distributes active quotas, and deals with any questions that may arise during the implementation of the treaty.

The 2nd Review Conference for the Open Skies Treaty was held in Vienna from June 7-9, 2010, under the chairmanship of the United States. The Conference’s Final Document paved the way for the use of digital cameras and sensors in the future by requesting states-parties consider the technological and financial aspects of converting to digital systems. The document also encouraged the expansion of the Open Skies Treaty to other countries, particularly those in the Organization for Security and Cooperation in Europe, where the OSCC is headquartered.

Images of Open Skies flights are available here.



1. Belarus, Belgium, Bosnia and Herzegovina, Bulgaria, Canada, Croatia, the Czech Republic, Denmark, Estonia, Finland, France, Georgia, Germany, Greece, Hungary, Iceland, Italy, Latvia, Lithuania, Luxembourg, the Netherlands, Norway, Poland, Portugal, Romania, Russia, Slovakia, Slovenia, Spain, Sweden, Turkey, Ukraine, the United Kingdom, and the United States (though the Trump administration withdrew the United States from the treaty in November 2020). Kyrgyzstan has signed, but not ratified the treaty.

2. For example, Russia, which shares its quota with Belarus, and the United States both have quotas permitting 42 flights per year, while Portugal is only obligated to allow two flights annually. Countries are not required to exhaust their flight quotas. In 2009, the United States flew a total of thirteen flights, twelve over Russia and one over Ukraine.

3. This limit can be extended by 24 hours if the host insists that the observing party use the host's aircraft and demonstration flight is conducted.