Background: Despite theoretical rationale and empirical evidence that suggests peer network gender norms may influence men’s perpetration of intimate partner violence (IPV), no studies have examined this association in sub-Saharan Africa. Grounded in social learning theory, social influence theory, and the theory of gender and power, the aims of this dissertation were to assess the degree to which peer network gender norms are associated with men’s perpetration of IPV, test whether the social cohesion of peer networks moderates this relationship, and to qualitatively explore whether and how peer networks influence men’s perpetration of IPV. Methods: I conducted two studies using quantitative and qualitative data from an ongoing HIV and IPV prevention trial, Vijana Vijiweni II, in Dar es Salaam, Tanzania. In the first study, I used multilevel logistic regression to analyze baseline data from sexually active men (n = 1,103) nested within 59 peer networks enrolled in the parent trial. In the second study, I collected qualitative in-depth interviews (n = 40) with a sub-sample of 20 men who reported perpetrating IPV in the first study and analyzed the data by generating narrative summaries and conducting thematic and interpretative coding. Results: Men in peer networks with increasing levels of inequitable peer network gender norms had over twice the odds of perpetrating physical IPV within the last year (OR=2.33, p = .04), controlling for demographic characteristics and individual-level attitudes towards gender roles. Peer network social cohesion significantly moderated the positive association between inequitable peer network gender norms and IPV perpetration such that the relationships grew stronger as cohesion increased. In the qualitative interviews, we saw no evidence that men self-selected into peer networks with certain characteristics. Rather, men described several mechanisms through which their peer networks influenced IPV perpetration behavior, including (1) men’s internalization of peer network norms, (2) men feeling pressure to conform to peer network norms, and (3) the direct involvement of peer networks in shaping couple power dynamics. Conclusions: Taken together, these findings suggest that peer network gender norms influence men’s perpetration of intimate partner violence and should be targeted in future gender-transformative interventions.