Apollo 8, the second crewed mission in the American Apollo space program, was the first human spaceflight to leave Earth orbit; the first to be captured by and escape from the gravitational field of another celestial body; and the first crewed voyage to return to Earth from another celestial body—Earth's Moon. The three-man crew of mission Commander Frank Borman, Command Module Pilot James Lovell, and Lunar Module Pilot William Anders became the first humans to travel beyond low Earth orbit, the first to see Earth as a whole planet, and then the first to directly see the far side of the Moon. The 1968 mission, the first crewed launch of a Saturn V rocket, was also the first crewed launch from the John F. Kennedy Space Center, Florida, located adjacent to Cape Canaveral.

Originally planned as a second Lunar Module/Command Module test in an elliptical medium Earth orbit in early 1969, the mission profile was changed in August 1968 to a more ambitious Command Module-only lunar orbital flight to be flown in December, because the Lunar Module was not yet ready to make its first flight. This meant Borman's crew was scheduled to fly two to three months sooner than originally planned, leaving them a shorter time for training and preparation, thus placing more demands than usual on their time and discipline.