This chapter summarizes the principles of mental health services organization. It describes the different types of mental health services, and discusses the main issues related to the development of integrated mental health systems. Mental health services are the means by which effective interventions for mental health are delivered, and are vital in reducing some of the burden of mental disorders. In the module Organization of services for mental health, the World Health Organization (WHO) broadly describes the way mental health services are organized around the world. The various components of mental health services are categorized as mental health services integrated into the general health system (in primary care and in general hospitals), community mental health services, and institutional mental health services (specialist institutional services and mental hospitals). The integration of mental health services into general health services is the most viable strategy for extending mental health services to underserved populations.