As part of the Apollo program by NASA, 24 astronauts flew nine missions to the Moon between December 1968 and December 1972. During six successful two-man landing missions, twelve men walked on the lunar surface, six of whom drove Lunar Roving Vehicles as part of the last three missions. Three men have been to the Moon twice, one orbited once and took a circumlunar trajectory the second time, while the other two landed once apiece. Apart from these 24 men, no human being has gone beyond low Earth orbit. As of November 2025^[update], five of the 24 remain alive. A number of non-human animals have circled or orbited it, including two tortoises, several turtles, and five mice.

Apollo missions 8 and 10–17 were the nine crewed missions to the Moon. Apollo 4–6 and AS-201 and AS-202 were uncrewed, while AS-203 is considered a test flight. The Apollo program included three other crewed missions: Apollo 1 (AS-204) did not launch and its crew died in a ground-based capsule fire, while Apollo 7 and Apollo 9 were low Earth orbit missions that tested spacecraft components and docking maneuvers. Apollo missions 18, 19, and 20 were canceled. Twelve astronauts later flew unused Apollo command modules in the Apollo Applications Program's Skylab and Apollo–Soyuz Test Project. Of the 24 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 commanded orbital Space Shuttle missions.

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 arrhythmia – 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.

The prime crew members selected for actual missions are here grouped by their NASA astronaut selection groups, and within each group in the order selected for flight. Two versions of the Apollo Command/Service Module (CSM) spacecraft were developed: Block I, intended for preliminary low Earth orbit testing; and Block II, redesigned for the lunar landing. The Block I crew position titles were Command Pilot, Senior Pilot (second seat), and Pilot (third seat). The corresponding Block II titles were: Commander, Command Module Pilot, and Lunar Module Pilot. The second seat pilot was given secondary responsibility for celestial navigation to keep the CSM's guidance computer accurately calibrated with the spacecraft's true position, and the third seat pilot served as a flight engineer, monitoring the health of the spacecraft systems.

All of these astronauts flew on Gemini, and except for White, each commanded one Gemini and one Apollo mission:

This was the first class of astronauts for which test pilot experience was not required, but military jet fighter pilot experience was acceptable.

Five of this group got their first spaceflight experience as second seat on Gemini:

The remaining six members of this group were selected for their first space flights on Apollo: