Mental health research is the study of the causes and correlates of mental health and illness, approaches to improve mental well-being, and the delivery of effective mental health services to those in need. Social workers have been leading researchers in each of these areas of inquiry, and this article provides an overview of the broad field of mental health research, with particular emphasis on the contributions of social work. A biopsychosocial review of research on the correlates of mental health and illness is provided, followed by a synthesis of studies examining pharmacological and psychosocial approaches to improving mental health. Research on mental health services is then presented, with a focus on studies seeking to improve access to quality care and reduce service disparities. Key directions for future mental health research include identifying specific causal predictors of mental illness, improving existing treatments, and disseminating advances to the community.