The author opens the subject by questioning "why" and "how" to plan for mental health. Planification is a public health process. This process made modern countries able to develop health care policies in accordance to scientific progress. This allowed to stop the transmission of communicable diseases. Mental health disorders are one of the 4 public health priorities along with cardio-vascular diseases, cancers an consequences of accidents. New care methods have to be found in order to be adapted to recent needs. In many countries, mental health care have been and still are on the way to be modified. These major modifications will be illustrated by the French "sectorisation" which will be replaced in the context of complete reconversion of the French mental health care system. Two research streams will be proposed: research focused on the health care system which will enlight the different systems, their characteristics, activities and adequation; epidemiological studies in order to measure population needs in term of mental health, to clarify how mental health disorders appear and what sort of care are used by the persons. To illustrate these themas, the author will present his own experience. For more than 25 years he was operating on complex private mental health care system using the resources of an epidemiological unit in order to plan the development of this care system.