Soyuz TM-21 was a Soyuz mission, a human spaceflight mission transporting personnel to the Russian space station Mir. Part of the US/Russian Shuttle-Mir Program, the mission launched from Baikonur Cosmodrome, atop a Soyuz-U2 carrier rocket, at 06:11:34 UTC on March 14, 1995. It is of note because its launch marked the presence, for the first time ever, of thirteen humans in space simultaneously - three aboard the Soyuz, three aboard Mir and seven aboard Space Shuttle Endeavour, flying STS-67.

The Soyuz is a Soviet crewed spacecraft, developed to perform lunar missions with crew. 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 on the Moon during the flight of Zond 5, with two turtles. Thereafter, it is adapted to the low orbit and will fly on the Soyuz launcher to supply the Soviet Salyut and Mir stations, and the ISS.