Computer science and artificial intelligence are increasingly used in the hazardous and uncertain realms of medical decision making, where small faults or errors can spell human catastrophe. This book describes, from both practical and theoretical perspectives, an AI technology for supporting sound clinical decision making and safe patient management. The technology combines techniques from conventional software engineering with a systematic method for building intelligent agents. Although the focus is on medicine, many of the ideas can be applied to AI systems in other hazardous settings. The book also covers a number of general AI problems, including knowledge representation and expertise modeling, reasoning and decision making under uncertainty, planning and scheduling, and the design and implementation of intelligent agents.The book, written in an informal style, begins with the medical background and motivations, technical challenges, and proposed solutions. It then turns to a wide-ranging discussion of intelligent and autonomous agents, with particular reference to safety and hazard management. The final section provides a detailed discussion of the knowledge representation and other aspects of the agent model developed in the book, along with a formal logical semantics for the language.