Book excerpt: Stress of either psychological or physical nature can activate and/or paralyse humans’ innate and adaptive immunity. However, adequate immunity is crucial to the maintenance of health on earth and in space. During space flight, human physiology and health are challenged by complex environmental stressors which might be at their most pronounced during lunar or interplanetary missions. While previous publications have addressed the physiological changes that occur during space flight, this book goes further, by adopting an interdisciplinary approach to analyze the complex interaction of living conditions in space, the immune system, and astronauts’ health. It is explained how such analysis of the consequences of stress for the immune system may help in preventing, diagnosing, and counteracting immune-related alterations in health on earth as well as in space