On May 30, 1975, the European Space Agency officially opened for business.
The European Space Agency was created as a merger of the European Launcher Development Organization, or ELDO, and the European Space Research Organisation, ESRO. Both ELDO and ESRO were established in the 1960s to unify the space-related activities of European nations.
After World War II, a lot of European rocket scientists left to work in the United States. This made it difficult for small countries in Europe to compete with the space programs of the U.S. and the Soviet Union, which were the two big superpowers in the world of spaceflight.
So, the Europeans united to create ELDO and ESRO. ELDO handled launch operations while ESRO handled the science. In 1975, they decided to unite those two organizations as well. The European Space Agency was officially founded with the signing of the ESA Convention on May 30, 1975, and the agency began operations the next day.