This mission was the seventh Soviet attempt to recover soil samples from the surface of the Moon and the first after the success of Luna 16.

After two midcourse corrections on 4 and 6 September 1971, Luna 18 entered a circular orbit around the Moon on 7 September at 100 kilometers altitude with an inclination of 35°. After several more orbital corrections, on 11 September, the vehicle began its descent to the lunar surface.

Unfortunately, contact with the spacecraft was abruptly lost at 07:48 UTC at the previously determined point of lunar landing. Impact coordinates were 3°34' north latitude and 56°30' east longitude, near the edge of the Sea of Fertility. Officially, the Soviets announced that "the lunar landing in the complex mountainous conditions proved to be unfavorable."