The NASA Mercury programme bridged the gap between the hypersonic X-15 and the two-man Gemini spacecraft, which in turn led to the Apollo spacecraft. This Manual completes the Haynes Workshop manual series of US and Russian piloted space vehicles. The Mercury programme began in 1958, with the goal of putting a man into Earth orbit and returning him safely, ideally before the Soviet Union. Seven astronauts were selected to train for spaceflights on the Mercury programme, and they became known as the Mercury Seven. A number of unmanned flights were made prior to the first manned flight, a sub-orbital flight in May 1961, that put US astronaut Alan Shephard in space, before John Glen became the first American to reach Earth orbit in February 1962. This Manual provides in-depth engineering insight, and tells the story of the hardware, the missions and the men behind Project Mercury.