Launch from the Baikonur Cosmodrome; landing 225 km southeast of Dzheskasgan.

Soyuz 40 was the ninth Interkosmos mission (with Dumitru Prunariu, the first cosmonaut from Romania). Following a one day solo flight Soyuz 40 docked with the Salyut 6 space station on May 15, 1981 as final spacecraft. During the next days the crew performed common scientific work with the fifth resident crew.

Scientific research and experiments including exploration of the Earth magnetic field was done. Earth observations had to be delayed until the last day of this mission, when Salyut 6 at last passed over Romania in daylight. During this time the crew also tested the station's orientation system.