Based on achievements in clinical medicine, medical expertise of the flying personnel, ergonomics, human engineering and other life sciences, as well as on the experience gained by Intercosmos researchers, space psychology transformed during 1960-1988 into an independent scientific discipline. This new branch of science has the capability to formulate and resolve important theoretical and applied problems of crew selection and training, assessment of emotional status and work capacity, prevention and optimization of crew activities. The findings and observations made it possible for space psychology to develop psychological reliability criteria and consequently to maintain good mental health and high work capacity of crewmembers in long-term space missions.