The classification of diagnostic criteria for mental illnesses is a topic of worldwide import. Public Health Aspects of Diagnosis and Classification of Mental and Behavioral Disorders provides mental health service planners, clinicians and researchers with a better understanding of how the current state of mental health classification and diagnosis impacts public health care. In addition, it identifies how changes to our psychiatric diagnostic system could potentially help international mental health programs to better serve their patients and other stakeholders. This collection of technical reviews was presented at the World Health Organization–American Psychiatric Institute for Research and Education conference "Public Health Aspects of Diagnosis and Classification of Mental Disorders," one in a series of conferences collectively entitled "The Future of Psychiatric Diagnosis: Refining the Research Agenda." The objective of the conference was to review the public health implications of diagnosis and classification of mental disorders, and as such, the material is relevant to the ongoing development of the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) as well as the 11th edition of the International Classification of Diseases (ICD-1). This work is fundamental to the history of psychiatric classification and indispensable to those seeking to understand not only the development of nosological systems but the effects they have on patient populations around the world.