In past years, hundreds of space life sciences investigations have been conducted on board the Space Shuttle, Skylab, and Spacelab. Experiments are now conducted on board the ISS, where special laboratory equipment and experimental procedures are specifically designed for use in space. In addition, flight experiments must fit within physical limits of the spacecraft and its resource constraints. Yet, as many experiments as possible are to be conducted on each mission to achieve maximum scientific return. This chapter reviews the constraints of space life sciences missions and the step-by-step procedures “to fly” an experiment.