Soyuz 6 was part of a joint mission with Soyuz 7 and Soyuz 8 that saw the three Soyuz spacecraft in orbit together at the same time, carrying a total of seven cosmonauts. The crew of Georgi Shonin and Valeri Kubasov were meant to take high-quality movie photography of the Soyuz 7 and Soyuz 8 docking, but the rendezvous systems on all three spacecraft failed.

It is still not known exactly what the actual problem was, but it is often quoted as being a helium pressurization integrity test.

The crew was made up of Shonin and Kubasov, who carried out experiments in space welding. While welding, Kubasov almost burned through the hull of the vehicle's Living Compartment, which in the absence of spacesuits could have resulted in a catastrophic situation. The weld quality was said to be in no way inferior to that of Earth-based welds.
After eighty orbits of the Earth, they landed on 16 October 1969, 180 km northwest of Karaganda, Kazakhstan.

This is Soyuz's 12th flight, and 5th crewed flight.

The Soyuz is a Soviet crewed spaceship, developed to made manned lunar missions. This version called 7K will fly 4 times on the giant launcher N1, and several tens of times on Proton to fly over the Moon, which will be successful during the mission Zond 4. Soyuz will become the first spacecraft to transport living beings to the Moon during the flight of Zond 5, with two turtles. Subsequently, it is adapted to low orbit and will fly on the Soyuz launcher to serve the Salyut and Mir stations and the ISS.