Zond 5 was a spacecraft of the Soviet Zond program. In September 1968 Zond 5 travelled to the Moon in a circumlunar trajectory and became the first Moon mission to include animals and the first to return safely to Earth. The first terrestrial organisms to fly to the vicinity of the Moon included two Russian 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.