Human papillomavirus (HPV) has been linked to genital warts and multiple cancers affecting both men and women. Despite college students' high risk for HPV, their vaccination rates remain suboptimal. The current observational study examined the relationship between social norms and HPV vaccine intentions and potential mechanisms underlying this relationship among undergraduates. Participants (N = 190; 66.8% female) completed a survey assessing HPV vaccine social norms, attitudes, self-efficacy, and intentions. Three mediation analyses were conducted to examine whether self-efficacy and attitudes mediated the relationship between social norms (i.e., parents, friends, doctor) and intentions, controlling for demographic and health care covariates. Social norms were indirectly related to intentions through self-efficacy and attitudes in multiple models (ps < .05). Specifically, perceiving greater support for HPV vaccination from one's friends, parents, and doctor was related to greater HPV vaccine self-efficacy, which, in turn, was related to increased vaccine intentions. In addition, perceiving greater parental and doctor support for HPV vaccination was related to more favorable attitudes towards the vaccine, which, in turn, were related to increased vaccine intentions. Findings suggest potential targets for future interventions to promote HPV vaccination among young adults.