The Apollo-Soyuz Test Project (ASTP) (Russian: Экспериментальный полёт «Союз» - «Аполлон», Eksperimantalniy polyot Soyuz-Apollon, lit. "Experimental flight Soyuz-Apollo"), in July 1975, was the first joint U.S.-Soviet space flight, and the last flight of an Apollo spacecraft. Its primary purpose was as a symbol of the policy of dente that the two superpowers were pursuing at the time, and marked the end of the Space Race between them that began in 1957.

The mission included both joint and separate scientific experiments (including an engineered eclipse of the Sun by Apollo to allow Soyuz to take photographs of the solar corona), and provided useful engineering experience for future joint US-Russian space flights, such as the Shuttle-Mir Programme and the International Space Station

ASTP was the last manned US space mission until the first Space Shuttle flight in April 1981. It was also U.S. astronaut Donald "Deke" Slyton's only space flight. He was chosen as one of the original Mercury Seven astronauts in April 1959, but had been grounded until 1972 for medical reasons.