This study investigated the extent to which adolescents' personal normative attitudes (also referred to as personal norms) and perceived peer norms regarding bullying, sexual harassment, and bystander intervention predicted each step of the five-step bystander intervention model (i.e., Notice, Interpret, Accept Responsibility, Know how to Help, Act) for bullying and sexual harassment among two-hundred thirty-three high school students in the Northeastern United States. Interaction effects of gender, personal norms, and perceived peer norms were also assessed. As predicted, perceived peer norms moderated the relations between personal norms and all five bystander intervention steps. However, some effects differed by gender and some differed in direction from predictions. Students who were more anti-bullying/harassment scored higher on some bystander intervention steps when they also perceived their peers to be more anti-bullying and harassment, with some models showing gender differences between male and female students. Personal and perceived peer norms are related to adolescents' engagement in the bystander intervention model, suggesting that both norms should be targets of interventions encouraging youth to intervene in incidents of bullying and sexual harassment.