Defining 'mental illness' in mental health policy.

Mental health policy is shaped fundamentally by the definition of mental illness associated with the policy. Changing policies reflect changing definitions. At various times, the definition may be narrow or broad with respect to the scope of conditions covered by a specific policy. The priority accorded to impairment severity is the most crucial and enduring policy issue related to the definition of mental illness and the scope of that definition. This paper explores the role of definitions in framing mental health policy, using examples from the history of policy making over the past half-century.