The Open Skies Treaty: Background and
Issues
Updated January 15, 2021
The United States announced its intention to withdraw from the Treaty on Open Skies on May 22, 2020;
this withdrawal took effect on November 22, 2020. Russia has also announced its plans to withdraw,
noting that it would begin the domestic procedures for withdrawal on January 15, 2021, and would then
send the official notification to the other treaty parties.
The United States, Canada, and 22 European nations signed this treaty on March 24, 1992. It entered into
force on January 1, 2002, and had 34 members before the U.S. withdrawal. The parties permit unarmed
observation aircraft to fly over their entire territories to observe military forces and activities. The treaty is
designed to increase transparency, build confidence, and encourage cooperation among European nations.
The parties had conducted 1,500 observation flights through early October 2019. Some parties provide
their own aircraft, but they can also join overflights on aircraft provided by other nations. Both the
observing nation and observed nation have access to the data from each flight; other parties can purchase
copies of the data, so all can share information collected during all flights. According to the State
Department, the United States conducted nearly three times as many flights over Russia as Russia did
over the United States. Further, the parties can invite flights over their territories in special circumstances,
as Ukraine did in 2014, when Open Skies flights helped monitor activities along the Ukraine-Russian
border.
With the United States withdrawal from the Treaty, it will no longer participate in flights or share data
collected by others. Russian officials insisted that the remaining participants not share data collected on
Open Skies flights with the United States. They also indicated that they expected to continue to fly over
U.S. bases and facilities located on the territories of other treaty parties. After the other parties rejected
these conditions, Russia announced its plans to withdraw from the treaty.
Background
President Eisenhower proposed an Open Skies agreement in 1955 to reduce the risk of war. Before
satellites existed, aerial overflights provided information for both intelligence and confidence-building
purposes. The Soviet Union rejected the proposal because it considered overflights equal to espionage and
believed the United States had more to gain than it did. President George H. W. Bush revived the proposal
in May 1989. By this time, both the United States and Soviet Union collected intelligence with satellites
and remote sensors. As Europe emerged from the East-West divide of the Cold War, the United States
supported increased transparency to reduce the chances of military confrontation. The Open Skies Treaty
was one of three arms control arrangements—including the Vienna Document and the Conventional
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Armed Forces in Europe Treaty (CFE)—which could serve, as then-Secretary of State Baker noted, as
“the most direct path to greater predictability and reduced risk of inadvertent war.”
Key Provisions
Open Skies participants make all their territory accessible to overflights by unarmed fixed-wing
observation aircraft. They can restrict flights for safety concerns, but cannot impede or prohibit flights
over areas, including military installations that would otherwise be off-limits. In most cases, the nation
conducting the observation flight provides the aircraft and sensors; officials from the host nation
participate in the flight.
The nation conducting an observation flight must provide 72 hours’ notice before arriving in the host
country. This provides the host with time to suspend sensitive military exercises or activities. The
observation team presents a mission plan, specifying details including the route and altitude for the flight.
The host nation can propose changes to the mission plan, due to weather or flight safety considerations,
but it cannot deny access to any area of its territory.
Open Skies aircraft can be equipped with four types of sensors: optical panoramic and framing cameras
(for still photography) with a ground resolution of 30 centimeters (around one foot); video cameras with a
ground resolution of 30 centimeters; infrared line-scanning devices with a ground resolution of 50
centimeters (around 20 inches); and sideways-looking synthetic aperture radars (SARs) with a ground
resolution of 3 meters (around 8 feet). This equipment can collect basic information on military forces
and activities, but would not provide detailed technical intelligence. It also allows monitoring of military
and civilian infrastructure, such as industrial plants, airports, roads, and railway lines, but would not allow
recognition of sensitive details about items such as electronic equipment.
The participants can upgrade cameras and sensors as technology advances, as long as the capabilities
remain within treaty parameters. The party using the new technology must demonstrate that technology to
the others participants and receive consensus approval before they can transition to new cameras. Russia
has recently equipped its aircraft with electro-optical cameras, replacing film with digital cameras. In
2018, the United States blocked approval of Russia’s use of new cameras, delaying flights planned for
that year; it reversed this decision in late 2018, and flights resumed in 2019.
Russian Compliance
According to the U.S. State Department, Russia restricted access for Open Skies flights over Kaliningrad,
over Moscow, and along the border between Russia and the Georgian regions of South Ossetia and
Abkhazia. Russia reportedly also failed to provide priority flight clearance for Open Skies flights on a few
occasions. The United States raised these issues in the Open Skies Consultative Commission; some have
been resolved. Nevertheless, the United States responded to limitations imposed by Russia by limiting the
length of flights over Hawaii and removing access to two U.S. Air Force bases used during Russian
missions over the United States.
Benefits and Risks
When the United States first signed Open Skies, most analysts agreed that the treaty would provide little
information not already available from observation satellites. But supporters argued that the treaty could
still benefit the United States and its allies. For example, most treaty participants do not have observation
satellites, so, as former Secretary of State George Schultz noted, “Open Skies is their only means of
alleviating security concerns through timely overhead imagery.” This reduces the risk of
misunderstandings or crises that could involve the United States and contributes to “a more stable and
secure European continent.”

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In 1992, analysts asserted the treaty would create few risks for the United States because Russia could
collect more detailed information with observation satellites. Nevertheless, some U.S. military and
intelligence officials have since cautioned that better optical technology might allow Russia to overcome
weaknesses in its satellite surveillance capabilities. Others questioned these conclusions, noting that
Russia would operate commercially available cameras, with resolutions that are both within the bounds
established by the treaty and also less precise than those offered by commercial satellites.

Author Information

Amy F. Woolf

Specialist in Nuclear Weapons Policy




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