Apollo was the NASA program that sent the first humans to the Moon. From 1969 to 1972, a total of 6 spacecraft carrying 12 astronauts landed on the lunar surface. It was the only time humans have ever walked on another celestial body, and none have left Earth orbit since.
On 25 May 1961, just 20 days after Alan Shepard became the first American to fly into space, President John F. Kennedy addressed a joint session of Congress to ask for funding to start the ambitious program: "I believe that this nation should commit itself, to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to the Earth," Kennedy said. NASA met the goal on 20 July 1969, when Neil Armstrong stepped onto the surface during Apollo 11.
The program culminated in 1972 with Apollo 17. It cost roughly $257 billion in 2020 dollars and employed 400,000 Americans at its peak. In total, Apollo astronauts returned 382 kilograms of lunar rocks, core samples, and regolith from the lunar surface. The samples showed the Moon is a lifeless world that formed roughly 4.5 billion years ago, experienced catastrophic change 3.8 billion years ago, and has been relatively (though not completely) inactive since. Its rocks are chemically related to Earth, supporting the theory that the Moon was created when another large world impacted early Earth.
11 October 1968
The first crewed Apollo mission
21 December 1968
The first human visit to lunar orbit
3 March 1969
Testing the lunar module above Earth
18 May 1969
Dress rehearsal for the Moon landing
16 July 1969
The first crewed Moon landing
14 November 1969
A pinpoint landing in the Ocean of Storms
11 April 1970
A successful failure
31 January 1971
Reaching the lunar highlands
26 July 1971
Roving in the shadow of mountains
16 April 1972
Delighting in Descartes