Which mission was the first international crewed spaceflight?

The Apollo–Soyuz Test Project was the first international crewed spaceflight.

Launched in July 1975, the mission joined an American Apollo spacecraft with a Soviet Soyuz spacecraft in Earth orbit. The crews conducted joint experiments and symbolically shook hands through an international docking module.

The Apollo crew included Thomas Stafford, Vance Brand, and Deke Slayton. The Soyuz crew consisted of Alexey Leonov and Valeri Kubasov. The spacecraft docked on 17 July and separated two days later.

Although the mission was a Cold War cooperation project rather than a permanent partnership, it established procedures later used in multinational programs. The Shuttle–Mir missions came more than two decades afterward.