Adherence is defined as the extent to which a patient's behavior coincides with medical or prescribed health advice. Adherence is considered non-judgmental and is preferred over the term "compliance," which carries negative connotations and suggests blame for the patient. A major challenge in the field of psychiatry has been to understand why patients may or may not adhere to medication and other treatment recommendations. A comprehensive review of the literature on medication adherence among patients with psychiatric illnesses was conducted with the following objectives: (1) to better understand the impact of medication nonadherence, (2) to identify risk factors for medication nonadherence, and (3) to study interventions designed to improve patient adherence. The authors initially searched the Ovid Medline electronic database using the key words "medication adherence" and "compliance" to identify all articles written in the English language published through early 2008. This produced over 2000 references. The search was then narrowed to publications specific to psychotropic medication. The ultimate goal of the review was to increase awareness of this critical issue and to discuss strategies that the psychiatric clinician can implement to address patient adherence to prescribed medications. The authors chose to include articles that were deemed to be clinically useful to the practicing clinician.Studies that have specifically investigated adherence to psychiatric medications vary in the definitions of adherence and methodology that were used, making interpretation of results across studies difficult. Psychoeducational interventions have long been the mainstay of treatment for adherence problems. However, there is growing evidence that other approaches such as cognitive-behavioral strategies and motivational interviewing may be effective. Based on a comprehensive literature review, the authors recommend the following strategies for addressing adherence problems: focus on strengthening the therapeutic alliance; devote time in treatment specifically to address medication adherence; assess patients' motivation to take prescribed medications; and identify and address potential barriers to treatment adherence.