Vostok 3 was a spaceflight of the Soviet space program intended to determine the ability of the human body to function in conditions of weightlessness and test the endurance of the Vostok 3KA spacecraft over longer flights. Cosmonaut Andriyan Nikolayev orbited the Earth 64 times over nearly four days in space, August 11–15, 1962, a feat which would not be matched by NASA until the Gemini program (1965–1966).

Vostok 3 and Vostok 4 were launched a day apart on trajectories that brought the spacecraft within approximately 6.5 km (4.0 mi) of one another. The cosmonauts aboard the two capsules also communicated with each other via radio, the first ship-to-ship communications in space. These missions marked the first time that more than one crewed spacecraft was in orbit at the same time, giving Soviet mission controllers the opportunity to learn to manage this scenario.