The European Space Agency (ESA; pronounced /ˈiːsə/ EE-sə) is a 23-member international organisation devoted to space exploration. It has its headquarters in Paris and a staff of around 3,000 people globally as of 2025. ESA was founded in 1975 in the context of European integration. Its 2026 annual budget was around €8.3 billion.
The ESA human spaceflight programme includes participation in the International Space Station (ISS) and collaboration with NASA on the Artemis programme, especially manufacturing of the Orion spacecraft's European Service Module (ESM). ESA launches and operates uncrewed missions to the Moon, Mars, Jupiter, Venus, Mercury, the Sun, and various comets and asteroids. Other activities include space telescopes, Earth observation satellites, asteroid impact avoidance, telecommunication and navigation satellites, designing launch vehicles (e.g. Ariane 6 is operated through Arianespace with ESA sharing in the costs), and maintaining Europe's spaceport (the Guiana Space Centre in Kourou, French Guiana), as well as space safety and commercialisation.
The treaty establishing the European Space Agency reads:
"The purpose of the Agency shall be to provide for and to promote, for exclusively peaceful purposes, cooperation among European States in space research and technology and their space applications, with a view to their being used for scientific purposes and for operational space applications systems."
ESA is responsible for setting a unified space and related industrial policy, recommending space objectives to the member states, and integrating national programmes like satellite development, into the European programme as much as possible.
Jean-Jacques Dordain—ESA's Director General (2003–2015)—outlined the European Space Agency's mission in a 2003 interview:
"Today space activities have pursued the benefit of citizens, and citizens are asking for a better quality of life on Earth. They want greater security and economic wealth, but they also want to pursue their dreams, to increase their knowledge, and they want younger people to be attracted to the pursuit of science and technology.
I think that space can do all of this: it can produce a higher quality of life, better security, more economic wealth, and also fulfill our citizens' dreams and thirst for knowledge, and attract the young generation. This is the reason space exploration is an integral part of overall space activities. It has always been so, and it will be even more important in the future."At the ministerial council of 2025, ESA member states widened the agency's mandate to include defence. The resolution reads:
"ESA's intergovernmental framework provides the credentials and tools for developing space technologies and systems [...] for security and defence and to implement corresponding activities."
After World War II, many European scientists left Western Europe to work with the United States. Although the 1950s boom made it possible for Western European countries to invest in research and specifically in space-related activities, Western European scientists realised solely national projects would not be able to compete with the two superpowers. In 1958, only months after the Sputnik shock, Edoardo Amaldi (Italy) and Pierre Auger (France), two prominent members of the Western European scientific community, met to discuss the foundation of a common Western European space agency. The meeting was attended by scientific representatives from eight countries.
The Western European nations decided to have two agencies: one concerned with developing a launch system, ELDO (European Launcher Development Organisation), of which Renzo Carrobio di Carrobio became the first Secretary General from 1964 to 1971, and the other the precursor of the European Space Agency, ESRO (European Space Research Organisation), led by Pierre Auger. The latter was established on 20 March 1964 by an agreement signed on 14 June 1962. From 1968 to 1972, ESRO launched seven research satellites, but ELDO was not able to deliver a launch vehicle. Both agencies struggled with the underfunding and diverging interests of their participants.
The ESA in its current form was founded with the ESA Convention in 1975, when ESRO was merged with ELDO. ESA had ten founding member states: Belgium, Denmark, France, West Germany, Italy, the Netherlands, Spain, Sweden, Switzerland, and the United Kingdom. These signed the ESA Convention in 1975 and deposited the instruments of ratification by 1980, when the convention came into force. During this interval the agency functioned in a de facto fashion.
ESA launched its first major scientific mission in 1975, Cos-B, a satellite monitoring gamma-ray emissions in the universe, which was first worked on by ESRO. ESA collaborated with NASA on the International Ultraviolet Explorer (IUE), the world's first high-orbit telescope, which was launched in 1978 and operated successfully for 18 years. A number of successful Earth-orbit projects followed, and in 1986 ESA began Giotto, its first deep-space mission, to study the comets Halley and Grigg–Skjellerup. Hipparcos, a star-mapping mission, was launched in 1989 and in the 1990s SOHO, Ulysses, and the Hubble Space Telescope were all jointly carried out with NASA. Later scientific missions in cooperation with NASA include the Cassini–Huygens space probe, to which the ESA contributed by building the Titan landing module Huygens.
As the successor of ELDO, the ESA has also constructed rockets for scientific and commercial payloads. Ariane 1, launched in 1979, carried mostly commercial payloads into orbit from 1984 onward. The next two versions of the Ariane rocket family were intermediate stages in the development of a more advanced launch system, the Ariane 4, which operated between 1988 and 2003 and established the ESA as the world leader in commercial space launches in the 1990s. Although the succeeding Ariane 5 experienced a failure on its first flight in 1996, it has since firmly established itself within the heavily competitive commercial space launch market with 112 successful launches until 2023. In 1998, ESA started developing the small-lift launch vehicle Vega.
Astronauts from the future ESA member states have been joining Soviet space missions since 1978. The first ESA astronaut to fly to space was Ulf Merbold who joined the STS-9 mission of the American Space Shuttle in 1983, that carried the first European-built Spacelab laboratory module. The experience gained during the Spacelab programme was later instrumental in developing the International Space Station (ISS). Since then, ESA astronauts have been joining Space Shuttle flights, as well as Russian Soyuz flights to the Mir space station. During the 1980s and 1990s, ESA was considering developing its own crewed spacecraft Hermes and a small space station Columbus MTFF. These plans were later abandoned and instead, ESA joined the ISS programme with Columbus being repurposed as one of the station's laboratory modules and ESA astronauts flying to the station on American and Russian spacecraft.
The beginning of the new millennium saw the ESA become, along with agencies like NASA and JAXA, one of the major participants in space research. Although ESA had relied on co-operation with NASA in previous decades, changed circumstances, such as tough legal restrictions on information sharing under ITAR, led to decisions to rely more on itself and on cooperation with Roscosmos.
The agency continued its contribution to the International Space Station (ISS) programme with European astronauts joining assembly flights as well as long-term missions to the station. In 2008, ESA added its laboratory module Columbus to ISS and started launching the ATV cargo spacecraft. During the 2000s, ESA was considering cooperation with Russia on the proposed Kliper and CSTS crewed vehicles, but neither of these was developed.
Notable deep space missions during the 2000s included the agency's first Moon, Mars, and Venus orbiters: SMART-1, Mars Express, and Venus Express. ESA's Huygens probe, launched together with the NASA's Cassini mission in 1997, reached its destination in 2005 when it successfully landed on Titan, marking the farthest landing from Earth a spacecraft has ever made. The comet orbiter Rosetta launched in 2004 and performed multiple deep space flybys and observations during the decade, but wouldn't reach its destination until 2014.