Soyuz (Russian: Союз, IPA: [sɐˈjus], lit. 'Union') is a series of spacecraft which has been in service since the 1960s, having made more than 140 flights. It was designed for the Soviet space program by the Korolev Design Bureau (now Energia). The Soyuz succeeded the Voskhod spacecraft and was originally built as part of the Soviet crewed lunar programs. It is launched atop the similarly named Soyuz rocket from the Baikonur Cosmodrome in Kazakhstan.

Following the Soviet Union's dissolution, Roscosmos, the Russian space agency, continued to develop and utilize the Soyuz. Between the Space Shuttle's 2011 retirement and the SpaceX Crew Dragon's 2020 debut, Soyuz was the sole means of crewed transportation to and from the International Space Station, a role it continues to fulfill. The Soyuz design has also influenced other spacecraft, including China's Shenzhou and Russia's Progress cargo vehicle.

The Soyuz is a single-use spacecraft composed of three main sections. The descent module is where cosmonauts are seated for launch and reentry. The orbital module provides additional living space and storage during orbit but is jettisoned before reentry. The service module, responsible for propulsion and power, is also discarded prior to reentry. For added safety and aerodynamics, the spacecraft is encased within a fairing with a launch escape system during liftoff.

The first Soyuz mission, Kosmos 133, launched unmanned on 28 November 1966. The first crewed Soyuz mission, Soyuz 1, launched on 23 April 1967 but ended tragically on 24 April 1967 when the parachute failed to deploy on reentry, killing cosmonaut Vladimir Komarov. The following flight, Soyuz 2 was uncrewed. Soyuz 3 launched on 26 October 1968 and became the program's first successful crewed mission. The program suffered another fatal setback during Soyuz 11, where cabin depressurization during reentry killed the entire crew. These are the only humans to date who are known to have died above the Kármán line, the conventional definition of the edge of space.

Despite these early tragedies, Soyuz has earned a reputation as one of the safest and most cost-effective human spaceflight vehicles, a legacy built upon its unparalleled operational history. The spacecraft has served as the primary mode of transport for cosmonauts to and from the Salyut space stations, the Mir space station, and International Space Station (ISS).

Soyuz spacecraft are composed of three primary sections (from top to bottom, when standing on the launch pad):

The orbital and service modules are discarded and destroyed upon reentry. This design choice, while seemingly wasteful, reduces the spacecraft's weight by minimizing the amount of heat shielding required. As a result, Soyuz offers more habitable interior space (7.5 cubic metres, 260 cubic feet) compared to its Apollo counterpart (6.3 m³, 220 cu ft). While the reentry module does return to Earth, it is not reusable, a new Soyuz spacecraft must be made for every mission.

Soyuz can carry up to three crew members and provide life support for about 30 person-days.^{[citation needed]}