Research has shown that substantial numbers of mental health patients may be coerced into ‘voluntary’ treatment. This article examines the concept of coercion to address the concerns of social scientists, treatment providers, and policy makers to know when coercion into treatment has occurred. This logically takes precedence over the second important question of whether or not coercion is desirable in some situations. A review of the scientific research on coercion and related topics of freedom, control, and choice leads to a theoretical framework in which coercion is defined in terms of opportunities to choose among courses of action. Implications of this analysis are drawn for mental health service delivery, mental health policy, and mental health research.