Viking 1 was the first of two spacecraft, along with Viking 2, each consisting of an orbiter and a lander, sent to Mars as part of NASA's Viking program. The lander touched down on Mars on July 20, 1976, the first successful Mars lander in history. Viking 1 operated on Mars for 2,307 days or 2245 Martian solar days, the longest Mars surface mission until the record was broken by the Opportunity rover on May 19, 2010.

The Viking 2 mission was part of the American Viking program to Mars, and consisted of an orbiter and a lander essentially identical to that of the Viking 1 mission. Viking 2 was operational on Mars for 1281 sols. The Viking 2 lander operated on the surface for 1,316 days, or 1281 sols, and was turned off on April 12, 1980, when its batteries failed. The orbiter worked until July 25, 1978, returning almost 16,000 images in 706 orbits around Mars.