Mars 7 (Russian: Марс-7), also known as 3MP No.51P was a Soviet spacecraft launched to explore Mars. A 3MP bus spacecraft which comprised the final mission of the Mars programme, it consisted of a lander and a coast stage with instruments to study Mars as it flew past. Due to a malfunction, the lander failed to perform a maneuver necessary to enter the Martian atmosphere, missing the planet and remaining in heliocentric orbit along with the coast stage.

Mars 7 spacecraft carried an array of instruments to study Mars. The lander was equipped with a thermometer and barometer to determine the surface conditions, an accelerometer and radio altimeter for descent, and instruments to analyse the surface material including a mass spectrometer. The coast stage, or bus, carried a magnetometer, plasma traps, cosmic ray and micrometeoroid detectors, stereo antennae, and an instrument to study proton and electron fluxes from the Sun.

Built by Lavochkin, Mars 7 was the second of two 3MP spacecraft launched to Mars in 1973, having been preceded by Mars 6. Two orbiters, Mars 4 and Mars 5, were launched earlier in the 1973 Mars launch window and were expected to relay data for the two landers. However, Mars 4 failed to enter orbit, and Mars 5 failed after a few days in orbit.