This book is the realization of the idea to focus on the immune system and its complex activities as the target of diagnostic and individual therapeutical measures for patients hospitalized in surgical intensive care units. What must be done when the immune system is "ill" and life-threatening processes such as systemic inflammation, sepsis, and organ failure are induced? Todays intensive care management offers answers to this question based on the comprehensive scientific knowledge as well as the daily personal experience of the authors.