The human element is perhaps one of the most critical challenges presented by the Space Exploration Initiative (SEI). Whether living on the surface of the Moon or traveling to the planetary surface of Mars, crews will have to depend upon one another for long periods of time and live and work together in extremely isolated, confined, and high risk environments. How does one select crews for such conditions and what training is required? How can stress be monitored and what interventions are necessary to prevent behavioral and psychological problems? The best analogs for understanding crew dynamics and performance may be Antarctic expeditions and undersea experiences. Another important source of information is the Soviet long-duration space experiences. This paper reviews some of the available information from U.S. and Soviet spaceflight experiences to gain insights on selecting crews and maintaining productivity for the human exploration missions.