Launch from the Baikonur Cosmodrome; landing with Soyuz 29 spacecraft 180 km southeast of Dzheskasgan.

This spaceflight carried the third Interkosmos mission. Following a two day solo flight Soyuz 31 docked with the Salyut 6 space station on August 28, 1978. Cosmonauts Valeri Bykovsky and Sigmund Jähn were greeted by resident crew Vladimir Kovalyonok and Aleksandr Ivanchenkov when they docked at the aft port of the Salyut 6 space station. The visitors brought with them fresh onions, garlic, lemons, apples and other food for the long-duration crew, then in space for more than two months. In the next days common work with the second resident crew was performed.

The presence of the East German cosmonaut was seen as significant because of the presence of the MKF-6M camera on the space station, built by the Carl Zeiss works at Jena. Medical and biological experiments were carried out, including an audio experiment which tested sound and noise perception limits. An experiment called Berolina used the Splav furnace to process an ampoule of bismuth and antimonide with the material between two plates in the ampoule. The tree structure which resulted was four to six times larger than what had been produced on the ground. Another experiment tested using different photographic films on the station's interior.

Sigmund Jähn became the first German in space. The crew conducted several scientific experiments in the areas materials research, Earth exploration, atmosphere research, medicine and biology. Using the two melting furnaces on board new connections and semiconductor structures were made of lead and tellurium, crystal growths experiments were performed and even optical glasses were melted. Observations to environmental pollutions were also performed.

Life sciences experiments were performed in the fields of hearing sensitivity, time feeling and also tasting. Experiments to bacteria growth and for the development of single celled organisms had also been done. Science work of Earth exploration included earth photography and meteorological measurements.

The Soyuz 31 crew swapped craft with the Soyuz 29 crew so as to supply the long-duration crew with a fresh craft. On September 02, 1978, the engines of Soyuz 29 were tested, 25 experiment containers with 100 experimental results were transferred, along with exposed film, and seat liners and centering weights were exchanged.

The standard recovery procedure was changed with this flight, observers noted. In the past, the recovery of a civilian Salyut crew had been made on the orbit following the one which provided a nominal launch opportunity to Salyut. With this and subsequent flights, the landing occurred during the orbit which provided the nominal launch opportunity. The effect of this change was to have a landing window open some two to three days earlier than otherwise.