Identification and application of the current research evidence to a clinical problem is a goal reflected in professional codes and institutional mission statements. The use of expert opinions and traditions is no longer clinically or legally defensible in an era of using emerging evidence. Application of current research evidence is the emerging standard of care for all health care personnel, including psychiatric mental health care. The emergence of evidence-based practice as the new standard of care obliges all health care providers to use the latest research evidence. The need to make an intervention based on the highest level of evidence mandates that clinicians understand levels of research evidence and how the different classification systems of evidence compare. In this article, the levels of research evidence are reviewed to provide a framework for determining the best evidence to use as a basis for clinical interventions.