If the planet is ever terraformed, it will be done by Human Beings whose permanent residence and planetary affiliation will be Mars. The Martians will be us.

Carl Sagan, Cosmos (1980, p. 135)

Advances in the exploration and habitation of space environments over the last half-century have set the stage for long-duration expeditions beyond Earth orbit. A common feature of these initiatives will be extended stays by groups of humans in extraterrestrial habitats. The success of such endeavors depends on the behavioral health and performance effectiveness of multinational microsocieties living and working continuously in confined, isolated, and hazardous environments for extended periods of time.

The increasing durations of space missions and human habitation in space environments over the past four decades have presented a range of biomedical and behavioral challenges. These challenges have been met with remarkable success, often under adverse circumstances. The so-called human element, however, remains the most complex component in the design of long-duration missions into space. The imperatives of behavioral health and performance effectiveness therefore present major challenges to mis-