Bullying, cyberbullying, and sexual harassment can be impacted by both personal attitudes and perceived social norms, although few empirical studies on this topic have been conducted with high school students. In this cross-sectional study, 233 high school students completed measures about personal normative attitudes, perceptions of peer norms, and perpetration of bullying, cyberbullying, and sexual harassment. Consistent with social norms theory, students perceived themselves to hold more prosocial (i.e., antibullying/antisexual harassment) personal normative attitudes than they perceived the typical student in their school to hold (i.e., peer norms). Path analyses revealed that students' personal normative attitudes (e.g., antibullying/antiharassment) were negatively related to their bullying, cyberbullying, and sexual harassment perpetration, although perceived peer norms were negatively related to sexual harassment perpetration only. Multiple-group path analysis revealed significant gender differences. Personal normative attitudes related to females' behavior for all forms of perpetration and only sexual harassment and cyberbullying for males (with more antibullying/antiharassment attitudes relating to less perpetration), although associations for males were stronger. Perceived peer norms related to bullying perpetration for males only. Results are discussed with regard to social-cognitive and peer contextual factors and implications for social norms interventions. [For the corresponding grantee submission, see ED618718.]