The Soyuz 40 mission was a 1981 Soviet crewed spaceflight and the final flight of the Soyuz 7K-T spacecraft. It was a collaboration between the Soviet Union and Romania.^[1]

Position	Crew
Commander	Leonid Popov Second spaceflight
Research Cosmonaut	Dumitru Prunariu Only spaceflight

Position	Crew
Commander	Yuri Romanenko
Research Cosmonaut	Dumitru Dediu

• Mass: 6800 kg
• Perigee: 198.1 km
• Apogee: 287 km
• Inclination: 51.6°
• Period: 89.06 minutes

Soyuz 40 was the 16th expedition to Salyut 6 and carried the ninth international crew. It also ended the first phase of the Intercosmos program by carrying Romanian cosmonaut Dumitru Prunariu and Soviet cosmonaut Leonid Popov to the station. In all, nine Intercosmos missions were launched between 1978 and 1981.

Soyuz 40 was the last of the original Soyuz spacecraft (due to its replacement by the Soyuz-T) and the last Soyuz spacecraft to dock with Salyut 6. During the crew's stay, Prunariu studied the Earth's magnetic field. Earth observations had to be delayed until the last day of the flight, when Salyut 6 passed over Romania in daylight. During this time the crew also tested the station's orientation system.

• List of human spaceflights to Salyut space stations
• List of Salyut expeditions