Updated July 19, 2007—On July 20, 1969, half a billion people watched as Neil Armstrong became the first person to set foot on the moon.

"That's one small step for man, one giant leap for mankind," he said, before imprinting his boot in the lunar dust. The televised images were relayed to Earth from a camera mounted on a leg of the Apollo 11 lunar module. Armstrong was joined on the moon by fellow crewmember Edwin "Buzz" Aldrin. Above them a third astronaut, Michael Collins, orbited in the mission's command module.

Armstrong and Aldrin spent only a few hours on the moon setting up some simple experiments. They left their footprints, a United States flag, and a plaque that reads: "Here men from the planet Earth first set foot on the Moon—July 1969 A.D.—We came in peace for all mankind."

Only 12 people have walked on the moon, the last two in December 1972. In 2004 U.S. President George W. Bush committed the country to a return to the moon, starting with a robotic mission by 2008 and a human mission as early as 2015 (see pictures of the next-generation craft for carrying humans to the moon). The plan is to eventually use the moon as a stage in missions to Mars and beyond.

—David Braun