In this chapter a review is given of astronaut selection campaigns carried out to date. The initial selections were undertaken in the United States and the Soviet Union. In the beginning the candidates were predominantly men having military backgrounds. Male engineers and doctors followed. With the exception of one occasion in the early 1960s, it was not until around 1980 that women were admitted as astronaut candidates. They have remained a minority. Nowadays Europe, Canada, Japan, and China also have corps of astronauts. The selection processes are long and thorough to ensure that the healthiest and most psychologically stable individuals are selected, with the potential to work well in a team while confined in a small space for extended periods of time. Having been selected, the candidates have a long and diverse training regime which requires flexibility and adaptability of both them and their families. The ultimate prize of a trip into space is not guaranteed, and the waiting period can be long. Intricate planning of space missions, which starts long before a mission occurs, produces detailed work schemes for the astronauts to follow when they are finally in space.