The impact of the human-environment interface on human performance during long-term space missions has been a major focus of attention over the last thirty years. Human factors requirements necessary for operational productivity and comfort have been the subject of numerous investigations. In this paper, some of the more significant findings are reviewed,with a view towards identifying areas of human factors/ergonomics which remain problematic and in need of further study. Special attention is directed towards the study of issues related to crew workload during long term space missions. The further application and potential of task network computer modeling tools is briefly discussed.