Multi-agent systems are one of the most exciting research areas in Artificial Intelligence. In the last ten years there has been a growing interest in the application of agent-based systems in health care. Moreover, a growing European community of researchers interested in the application of intelligent agents in health care emerged as a result of the activities within the AgentCities.NET European network and the AgentLink III Technical Forum Group on Healthcare Applications of Intelligent Agents. And specially in RandD projects funded during the FP6. Thus, this book reports on the results achieved in this area, discuss the benefits (and drawbacks) that agent-based systems may bring to medical domains and society, and also to provide a list of the research topics that should be tackled in the near future to make the deployment of health-care agent-based systems a reality. Current topics of research include communication and co-operation betweendistributed intelligent agents to manage patient care, information agents that retrieve medical information from the Internet, and multi-agent systems that assist the doctors in the tasks of monitoring and diagnosis. A lot of methodological and technical problems are beginning to be discovered by the researchers that attempt to deploy agent-based systems in the medical area; just to name a few, there does not exist a universally accepted standard medical ontology, it is difficult to integrate new agent systems with legacy software, and these new agent-based systems should take into account rapidly changing national and international laws and regulations concerning the privacy of medical data and the security of the transaction of patient information between agents. The reader will find a comprehensive view of the field and up-to-date state-of-the-art of the research in this field in Europe.