The proposals for the chapter dealing with mental, behavioural and developmental disorders in the tenth revision of the International Classification of Diseases (ICD) are in the true sense a product of many minds. In their development WHO has called on and received the generous advice and support of its network of collaborating centres, of the members of Expert Advisory Panels on Mental Health, Neurosciences and Drug Dependence and Alcohol Problems from some 60 countries, and of the non-governmental organizations with whom WHO is in official relations. Among the latter, the collaboration with the World Psychiatric Association has been particularly useful; this Association sent the text of the ICD to all of its member societies, assembled their views and comments and worked closely with WHO in incorporating these comments into the text of the ICD. The WPA has created a special committee under the chairmanship of Professor E. Stromgren which summarised all the views received, and maintained collaboration with WHO throughout the development of the proposals.