Soyuz 8 (Russian Союз 8, Union 8) was part of a joint mission with Soyuz 6 and Soyuz 7 that saw three Soyuz spacecraft in orbit together at the same time, carrying seven Cosmonauts.

The crew consisted of commander Vladimir Shatalov and flight-engineer Aleksei Yeliseyev, whose mission was to dock with Soyuz 7 and transfer crew, as the Soyuz 4 (involving, among others, these two cosmonauts) and Soyuz 5 missions did. Soyuz 6 was to film the operation from nearby.

However, this objective was not achieved due to equipment failures. Soviet sources were later to claim that no docking had been intended, but this seems unlikely, given the docking adapters carried by the spacecraft, and the fact that both Shatalov and Yeliseyev were veterans of the previous successful docking mission. This was the last time that the Soviet crewed Moon landing hardware was tested in orbit, and the failure seems to have been one of the final nails in the coffin of the programme.

The radio call sign of the spacecraft was Granit, meaning Granite. This word is apparently used as the name of a reactive or defensive squadron in Soviet military training, and, just like the Soyuz 5, it was constructed and its crew was trained to be the responsive (not entirely passive) or female spacecraft in its docking. Giving military names to the spacecraft was probably a response to an appeal that the commander of the Soyuz 5 made. Further, the word was probably chosen as it begins with a letter following that sequence starting with Antey (meaning Antaeus) and Buran (meaning Blizzard); Г (G) is the fourth letter of the Russian alphabet.

The mission objectives included:
-checkout and flight test of spaceborne systems and the modified structure of the Soyuz craft,
-further improvement of the control, orientation, and orbital stabilisation systems and navigation aids,
-debugging the piloting systems by orbital maneuvering of the spaceships in relation to one another,
-testing of a system for control of the simultaneous flight of three spacecraft,
-scientific observations and photographing of geological-geographical subjects and exploration of the Earth's atmosphere,
-studying circumterrestrial space,
-conducting experiments of engineering research and biomedical engineering importance.

With all three Soyuz spacecraft finally in orbit, the stage was set on October 14, 1969, for the docking between Soyuz-7 and Soyuz-8, followed by the approach of Soyuz-6 to as close as 50 meters from the docked pair.

All necessary orbit corrections for the long-range rendezvous went as planned, allowing Soyuz-8 to begin the approach to Soyuz-7 from an initial distance of around 250 kilometers. By the end of the automated rendezvous process, the two ships came no farther than one kilometer from each other, but the Igla rendezvous system aboard Soyuz-8 failed to make the radio capture of Soyuz-7 necessary to perform the final approach and docking.

According to recollections from Nikolai Kamanin and Boris Chertok, the cosmonauts on both sides saw each other's ships and were ready to complete the linkup manually, but Shatalov first requested from the ground permission to do so. In the tense atmosphere of the main ground control station in Crimea, Mishin hastily discussed the situation with Chertok and other specialists and gave the green light to the manual attempt on the condition that the ships be not farther than 1.5 kilometers from each other. The flight managers were apparently concerned that an attempt to manually control the vehicle from a greater distance without adequate navigation aids and without the ability of mission control to carefully monitor the progress of the rendezvous could lead to overspending of propellant and even endanger the return to Earth.

Mishin quizzed Armen Mnatsakanyan, the top official responsible for the automated rendezvous system, whether the faulty Igla system could be jump-started but to no avail.

After two failed attempts at rendezvous, the mission control considered alternative ways of saving the flight program, as the spacecraft trio went out of range of communications with Soviet ground stations for several orbits. Experts in ballistics proposed a new series of high-precision orbital correction maneuvers under careful guidance from the ground, which could bring the vehicles close enough for Shatalov to perform manual rendezvous and docking.

According to Kamanin, by 12:40 Moscow Time, Soyuz-8 and Soyuz-7 came within 1,700 meters and the crews began manual rendezvous maneuvers. (Mission control saw that Shatalov aboard Soyuz-8 had activated the propulsion system four times. Again, both crews saw each other's ships, but, one more time, without reliable data on the mutual position and the rendezvous rates, Shatalov was unable to perform the necessary maneuvers to cross the divide. Instead, the ship's began drifting apart. Mishin's notes indicate that at 15:30 Moscow Time, the vehicles were 1.5 kilometers apart and moving with a relative speed of 1.5 meters per second.

Before the conclusion of the workday on October 15, Soyuz-6 piloted by Shonin approached as close as 800 meters from Soyuz-7, but, unlike Shatalov's Soyuz-8, Soyuz-6 had no docking port to dock. Still, Shonin earned praises from the ground for his excellent maneuvering skills.