What is psychiatry, and how does it relate to other medical and mental health disciplines? Apart from the obvious sociological answer—psychiatrists are physicians who have completed residency training in psychiatry—psychiatry has always struggled to define itself with precision. Unlike pediatrics or geriatrics, psychiatry does not define itself by reference to a specific demographic population. Unlike general surgery or anesthesiology or radiology, it does not define itself exclusively with reference to specific technologies or interventional practices: the majority of psychotropic medications in the United States are prescribed by nonpsychiatrists [1]. Unlike certain medical specialties such as nephrology or cardiology, psychiatry cannot lay exclusive claim to a particular body part or organ system: although psychiatry is often referred to as a "clinical neuroscience" [2], psychiatry at best shares this distinction with neurology, neurosurgery, and neuropsychology. Nor can psychiatry define itself according to a particular institutional structure of practice, since psychiatrists have long shed their historic identification with inpatient institutions and now work within a broad and diverse array of practice settings.