The modern development of medicine has been characterized by the grow ing use of new technologies in health care delivery and research. As an empirical science, medicine is based on many types and quantities of information to recognize alterations, explore causes and apply cor rective action. Dealing with biological objects, signals have to be collected, processed and interpreted to recognize the state of this object. It is therefore understandable that data processing technology and informatics have been employed to a growing extent in medicine. The increasing economic repercussions of modern medicine lead also to the demand of ways and means to assess the system as such and to develop means for evaluation and regulation. However, the application of data processing to the medical field has very often grown in parallel to and remote from the development of in formatics and data processing in general. Furthermore, difficulties have occurred resulting from the differing concepts of reasoning, deci sion making and methodology. We therefore decided to start a series of seminars with the attempt to bring scientists from both medicine and informatics together to discuss basic principles of informatics and medicine and to attempt a synthesis between the problems in medicine and health care delivery and methods in informatics to approach a solu tion of these problems. This volume contains the lecture notes of the first seminar of this type.