Proton (Russian: Протон) (formal designation: UR-500) is an expendable launch system used for both commercial and Russian government space launches. The first Proton rocket was launched in 1965. Modern versions of the launch system are still in use as of 2022, making it one of the most successful heavy boosters in the history of spaceflight. The components of all Protons are manufactured at the Khrunichev State Research and Production Space Center factory in Moscow and Chemical Automatics Design Bureau in Voronezh, then transported to the Baikonur Cosmodrome, where they are assembled at Site 91 to form the launch vehicle. Following payload integration, the rocket is then brought to the launch pad horizontally by rail, and raised into vertical position for launch.

As with many Soviet rockets, the names of recurring payloads became associated with the launch vehicle itself. The moniker "Proton" originates from a series of similarly named scientific satellites, which were among the rocket's first payloads. During the Cold War, it was designated the D-1/D-1e or SL-12/SL-13 by Western intelligence agencies.

Launch capacity to low Earth orbit is about 22.8 tonnes (50,000 lb). Geostationary transfer capacity is about 6.3 tonnes (14,000 lb). Commercial launches are marketed by International Launch Services (ILS).

In 2013, the rocket was intended to be retired before 2030.

As of June 2018, production on the Proton rocket is ceasing as the new Angara launch vehicle comes on line and becomes operational. No new launch service contracts for Proton are likely to be signed.