Colleges and universities are high-risk settings for sexual and relationship violence. To address these problems, institutions of higher education have implemented prevention programs, many of which train students as potential bystanders who can step in to help diffuse risky situations, identify and challenge perpetrators, and assist victims. The impact of bystander sexual and relationship violence prevention programs on long-term behavior of bystanders has remained a key unanswered question for those who seek to offer the most effective programs as well as for policy makers. In this study, the researchers experimentally evaluated the effectiveness of the Bringing in the Bystander® in-person program. Participants were 948 1st-year college students of whom 47.8% were women and 85.2% identified as White (15% also identified as Hispanic in a separate question) between the ages of 18 and 24 at two universities (one a rural, primarily residential campus and the other an urban, highly commuter campus) in the northeastern United States. To date, this is the first study to have found positive behavior changes as long-lasting as 1 year following an educational workshop focusing on engaging bystanders in preventing sexual and relationship violence. Even so, many questions remain to be answered about prevention and intervention of this type. More prospective research is needed on bystander-focused prevention of these forms of violence to help understand and better predict the complicated relationships both between and among the attitudes and behaviors related to preventing sexual and relationship violence. In this regard, we make specific recommendations for designing and evaluating programs based on our findings relating to the importance of moderators, especially two key understudied ones, readiness to help and opportunity to intervene.