Project Gemini was the second United States human spaceflight program to fly. Conducted after the first American manned space program, Project Mercury, while the Apollo program was still in early development, Gemini was conceived in 1961 and concluded in 1966. The Gemini spacecraft carried a two-astronaut crew. Ten Gemini crews and 16 individual astronauts flew low Earth orbit (LEO) missions during 1965 and 1966.

Human spaceflight is spaceflight with a crew or passengers aboard a spacecraft, often with the spacecraft being operated directly by the onboard human crew. Spacecraft can also be remotely operated from ground stations on Earth, or autonomously, without any direct human involvement. People trained for spaceflight are called astronauts, cosmonauts (Russian), or taikonauts (Chinese); and non-professionals are referred to as spaceflight participants or spacefarers.