Thirty-two astronauts were assigned to fly in the Apollo manned lunar landing program. Twenty-four of them left Earth's orbit and flew around the Moon on nine missions. (Of the other manned missions, Apollo 1 did not launch and Apollo 7 and Apollo 9 were low Earth orbit spacecraft testing missions). In addition, nine astronauts flew Apollo spacecraft in the Apollo Applications Programs Skylab and Apollo–Soyuz Test Project.
Twelve of these astronauts walked on the Moon's surface, and six of those drove Lunar Roving Vehicles on the Moon. While three astronauts flew to the Moon twice, none of them landed on the Moon more than once. The nine Apollo missions to the Moon occurred between December 1968 and December 1972.
Apart from these twenty-four people who visited the Moon, no human being has gone beyond low Earth orbit. They have, therefore, been farther from the Earth than anyone else. They are also the only people to have directly viewed the far side of the Moon. The twelve who walked on the Moon are the only people ever to have set foot on an astronomical object other than the Earth.
Of the twenty-four astronauts who flew to the Moon, two went on to command a Skylab mission, one commanded Apollo–Soyuz, one flew as commander for Approach and Landing Tests of the Space Shuttle, and two went on to command orbital Space Shuttle missions. A total of 24 NASA astronauts from the Apollo era flew on the Space Shuttle.
NASA's Director of Flight Crew Operations during the Gemini and Apollo programs was Donald K. "Deke" Slayton, one of the original Mercury Seven astronauts, who was medically grounded in September 1962 due to a minor cardiac arrythmia – paroxysmal atrial fibrillation. Slayton was responsible for making all Gemini and Apollo crew assignments. In March 1972, Slayton was restored to flight status, and flew on the 1975 Apollo–Soyuz Test Project mission.