Increased awareness of the relational aspects of gender suggests that a comprehensive, evidence-based response to child marriage should engage not only women and girls but also the brothers, fathers, uncles, and future husbands and fathers-in-law of the girls who have been the focus of programmatic efforts. While girls are disproportionately affected by child marriage – being more likely than boys to marry as children and to have their schooling, peer contact and mobility limited by marriage – engaging men and boys is necessary for challenging harmful gender norms and increasing understanding of the myriad negative consequences of inequitable relationships. Yet the development community has paid only nominal attention to the role of men and boys in changing harmful marriage-related norms and, in most settings, has failed to address boys’ own vulnerabilities. This has arisen from a desire to focus on the rights and well-being of girls, but has limited the range of interventions used to end the practice of child, early, and forced marriages and unions (CEFMU).