3 http://dx.doi.org/10.1037/14862-001 APA Handbook of Clinical Psychology: Vol. 4. Psychopathology and Health, J. C. Norcross, G. R. VandenBos, and D. K. Freedheim (Editors-in-Chief) Copyright © 2016 by the American Psychological Association. All rights reserved. C HAPTER 1 CLASSIFICATION OF MENTAL AND BEHAVIORAL DISORDERS Geoffrey M. Reed, Rebeca Robles, and Tecelli Domínguez-Martínez The World Health Organization (WHO) deines a classiication of diseases as “a system of categories to which morbid entities are assigned according to established criteria” (WHO, 1992b, p. 3). WHO’s International Classification of Diseases and Related Health Problems (ICD) is by far the most widely used health classiication worldwide. The widespread use of the ICD around the world is based on WHO’s constitutional responsibilities and the obligations of its 194 member states (WHO, 2014). WHO is a specialized agency of the United Nations with global public health responsibilities deined by interna- tional treaty. Among these are the following: (a) establishing and revising international nomencla- tures of diseases, causes of death, and public health practices; and (b) standardizing diagnostic proce- dures as necessary. WHO member states, including the United States, agree to use the ICD as a basis for reporting health information so that it is internation- ally comparable. The ICD provides the structural framework and much of the conceptual basis for specialty classiications in a variety of areas, includ- ing oncology, dermatology, dentistry, neurology, rheumatology, orthopedics, pediatrics, and mental disorders, including the American Psychiatric Asso- ciation’s Diagnostic and Statistical Manual of Mental Disorders (DSM). The ICD also provides the basis for national government adaptations, such as the ICD–10 Clinical Modiication (ICD–10 CM), adopted in the United States as of October 1, 2015. The classiication of mental disorders contained in the ICD and other systems derived from it directly affects psychologists and has profoundly inluenced the discipline of clinical psychology and other men- tal health professions. Classiication systems are used as a basis to deine the impact and prevalence of mental disorders around the world, to deine which individuals are entitled to receive mental health services, for administrative management of health encounters (e.g., billing and reimbursement), for the collection and reporting of health informa- tion based on those encounters, and to deine pro- fessional scope of practice. Classiication systems are a foundational aspect of practice, research, educa- tion, and training in clinical psychology around the world. This chapter provides a brief history of mental disorders classiication, the ICD, and the relation- ship between the ICD and the DSM. It discusses the conceptual principles and conventions that underlie both of these classiication systems and that have given rise to important criticisms. Although much of the discussion in this chapter is related to both the DSM and the ICD, it focuses particularly on WHO’s current development of the classiication of mental and behavioral disorders in ICD–11, scheduled for approval by the World Health Assembly in 2018. The ICD–11 is less familiar to clinical psychologists in the United States than similar information about the DSM–5 (American Psychiatric Association, 2013), about which much has already been writ- ten. Therefore, this chapter focuses on how WHO’s global public health priorities are informing the development of the ICD–11 classiication of mental disorders and the nature of the diagnostic guidance provided. The closing section, Future Directions, COPYRIGHT AMERICAN PSYCHOLOGICAL ASSOCIATION. NOT FOR DISTRIBUTION