Zond 5 (Russian: Зонд 5, lit. ‘Probe 5’) was a spacecraft of the Soviet Zond program. In September 1968 it became the second spaceship to travel to and circle the Moon, and the first to return safely to Earth. Zond 5 carried the first terrestrial organisms to the vicinity of the Moon, including two tortoises, fruit fly eggs, and plants. The tortoises underwent biological changes during the flight, but it was concluded that the changes were primarily due to starvation and that they were little affected by space travel.
The Zond spacecraft was a version of the Soyuz 7K-L1 crewed lunar-flyby spacecraft. It was launched by a Proton-K carrier rocket with a Block D upper-stage to conduct scientific studies during its lunar flyby.