Psychiatrists often contrast the biopsychosocial approach to mental illness with reductionism. However, what reduction in psychiatry might involve, what it entails for the biopsychosocial approach, and what its clinical implications might be, are questions that have not been satisfactorily addressed to date. On the contrary, psychiatrists' discussions of reductionism have often obscured these issues. The aims of this article are to consider some such discussions of reductionism, to disentangle and clarify some of the issues discussed, and to indicate how psychiatrists—particularly advocates of the biopsychosocial approach—might apply thought about reductionism usefully and productively.