As space missions become longer and broader in scope, and as crews become more heterogeneous, psychological and interpersonal factors will take on increasing importance. In order to isolate instructive psychosocial issues and trends, a review was made of over 60 American and Russian simulation and spaceflight studies and reports. Although the missions accomplished most of their goals, psychological and social stresses were evident in the crew members. Psychosocial problems tended to relate to mission length. There was evidence that the use of appropriate psychological testing and interpersonal sensitivity training could improve crew selection and ameliorate problems in the simulation studies. It is time to apply this knowledge to actual spaceflight conditions.