In recent years, the rising rate of suicides by military personnel has generated concern among policymakers, military leaders, and the public at large. Based on a recommendation from an earlier RAND report on preventing suicide among military personnel, this study reviews the literature on gatekeeper models of suicide prevention to better understand what is known about the effectiveness of gatekeepers and gatekeeper training. The study presents a theoretical model describing how gatekeeper training may influence individual knowledge, beliefs, and attitudes that may, in turn, result in intervention behaviors. It then reviews the evidence supporting each of the relationships presented in this model, and concludes with recommendations for advancing research in this field.