The classification of mental disorders improved greatly in the last decade of the 20th century and now provides a reliable operation tool. The first set of papers in this publication present the views on international classification and diagnosis of the WHO and the APA as well as the results of a large international survey on the usage and perceived value of ICD-10 and related diagnostic systems. The second group of papers topically review international experience with current diagnostic systems. The third set delves into some of the key conceptual bases for the development of future diagnostic systems. The fourth group review ongoing work on adaptations of and complements to the ICD. The last section offers incisive commentaries on integrative approaches and future steps. Summarizing the current knowledge of the field of the international system for classification and diagnosis this publication is essential reading for psychiatrists, psychologists as well as public health services.