A mental health information system is a system for collecting and applying information about a mental health service and the mental health needs of the population it serves. The module begins with a discussion of what information should be collected and how this information can be used. Based on the experiences of several countries in developing health information systems, the module articulates a number of broad principles that a country should adhere to in the development of a mental health information system. It then lays out a step-by-step approach to designing, establishing and evaluating such a system. Information systems are essential for both long-term national mental health planning and service delivery at community and individual levels. Also available: "WHO Mental Health Policy and Service Guidance Package--14 modules" Other modules included in the package: "Improving Access and Use of Psychotropic Medicines Child and Adolescent Mental Health Policies and Plans Mental Health Policy, Plans and Programmes. Updated version Mental Health Context Mental Health Financing Advocacy for Mental Health Quality Improvement for Mental Health Organization of Services for Mental Health Planning and Budgeting to Deliver Services for Mental Health Mental Health Legislation and Human Rights Mental Health Policies and Programmes in the Workplace Human Resources and Training in Mental Health Monitoring and Evaluation of Mental Health Policies and Plans"