Medicine of the mind, a highly interdisciplinary activity now known as psychiatry, was born in asylums concerned with the later stages of severe conditions that continue to shape even our most recent diagnostic classifications. Schizophrenia is the prototypical example. Despite this heritage, evidence-based approaches from clinical mental health sciences have alerted us to the potential benefits or early interventions to prevent such outcomes, while epidemiology has shown that less severe but common illnesses such as depression and anxiety are highly comorbid states that wax and wane in the population. Life course models now encompass developmental origins of health and disorder, and modern, multi-level concepts of causation offer the possibility of decisive preventative action. Psychiatry has shifted to the left, and prevention science has matured. What does the evidence tell us about prevention of mental disorders?