Sets out internationally-agreed diagnostic criteria specifically designed for use when conducting research on mental and behavioural disorders. Deliberately restrictive, the criteria are intended to facilitate the selection of groups of individuals whose symptoms and other characteristics resemble each other in clearly stated ways, and thus to maximize the homogeneity of study groups and the comparability of findings in multicentre and international studies. The book, which covers over 300 disorders, is derived from chapter V(F) of the Tenth Revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-10). The research criteria were developed in collaboration with the world's leading experts and finalized after testing by researchers and clinicians in 32 countries, representing all the major traditions and schools of psychiatry. Descriptions of clinical concepts upon which the research criteria are based are contained in the companion volume, Clinical Descriptions and Diagnostic Guidelines. For each disorder, criteria are labelled with letters or numbers to indicate their place in a hierarchy of generality and importance. This hierarchy includes general criteria, which must be fulfilled by all members of a group of disorders, obligatory criteria for individual disorders, and further groups and sub-groups of characteristics, of which only some are required for the diagnosis. Where appropriate, the most commonly used exclusion clause is also listed. A number of disorders of uncertain or provisional status are described in two annexes. The first covers affective disorders that have been the subject of recent research, together with certain personality disorders. The second describes several disorders that seem to appear almost exclusively in particular cultures.