12, all between 1969 and 1972. All American-born men and citizens. They are listed with the year of their landing and their age at the time:
1969: Neil Armstrong (38), Buzz Aldrin (39), Pete Conrad (39), Alan Bean (37).
1971: Alan Shepard (47), Edgar Michell (40), David Scott (39), James Irwin (38).
1972: John Young (41), Charles Duke (36), Eugene Cernan (38), Harrison Schmitt (37).
A further 12 individuals also circled the moon during the same period, but did not set foot on it.
Alan Shepard also has the distinction of being the first American astronaut (man in space), having flown in the Freedom 7 aircraft in 1961 to 116 miles above the Earth.
James Irwin was the first to drive a lunar rover on the Moon.
The USSR sent at least 20 manned missions to circle the moon, and has landed unmanned probes on the Moon. The Soviets achieved the first impact and first safe landing of probes on the moon. But no cosmonauts ever landed there.