Forecasts for future manned, space missions, beyond those typified by the Space Shuttle and Spacelab flights, as now defined, include various mission concepts that require teams of many human participants working and living in space for extended periods of time. Most of the concepts under discussion for the near term (1980-2000) involve space industrialization objectives of some type, and preliminary design and feasibility studies are increasing in number and scope. These potential missions may involve the order of tens of people in space for a period of months. In the early twenty-first century, it is conceivable that missions might involve hundreds of people in space for a period of years. With closed-environment life support technology yet in its infancy, it is timely to begin studies of technology requirements and design concepts to provide advanced life support systems that would be appropriate for such missions. The purpose of this paper is to present an overview of some major factors that will be associated with the design of these systems for operation in the space environment.