Soyuz 18 was a 1975 Soviet crewed mission to Salyut 4, the second and final crew to man the space station. Pyotr Klimuk and Vitaly Sevastyanov set a new Soviet space endurance record of 63 days and the mark for most people in space simultaneously (seven) was tied during the mission.

Salyut 4 was a Salyut space station launched on December 26, 1974 into an orbit with an apogee of 355 km, a perigee of 343 km and an orbital inclination of 51.6 degrees. It was essentially a copy of the DOS 3, and unlike its ill-fated sibling it was a complete success. Three crews attempted to make stays aboard Salyut 4. The second stay was for 63 days duration, and an unmanned capsule, called Soyuz 20, remained docked to the station for three months, proving the system's long-term durability despite some deterioration of the environmental system during Soyuz 18's mission. Salyut 4 was deorbited February 2, 1977, and re-entered the Earth's atmosphere on February 3.