The World Health Organization (WHO) is in the process of revising the International Statistical Classification of Diseases and Related Health Problems (ICD-10), approved in 1990. Since ICD-10’s approval, important new disease entities have emerged and medical and public health advances have contributed to new understandings of health and disease. The revision of the ICD-10 mental and behavioural disorders classification must make use of new knowledge in genetics, neuroscience, epidemiology, and cognitive and behavioural sciences to address systemic limitations. At the same time, it must be responsive to WHO’s public health mission and three core constituencies: member countries, multidisciplinary health professionals, and users of mental health services. Worldwide, most people with mental disorders still receive no treatment, and the primary public health objective is to increase coverage and enhance care. A reliable and accurate classification system can help to address public health needs, but must be usable and useful to front-line health providers who actually deliver care. A global, multidisciplinary, and multilingual revision process is focusing on global scientific evidence, worldwide clinical utility, and cross-cultural applicability. Special considerations in the revision include: harmonization of the ICD with the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders; the development of multiple versions of ICD mental and behavioural disorders classification; and careful consideration concerning inclusion of additional information relevant to patient assessment and care in the diagnostic manual.