Despite growing male participation in ending violence against women, little is known about the factors that precipitate men's engagement as antiviolence "allies." This study presents findings from a qualitative analysis of interviews with 27 men who recently initiated involvement in an organization or event dedicated to ending sexual or domestic violence. Findings suggest that men's engagement is a process that occurs over time, that happens largely through existing social networks, and that is influenced by exposure to sensitizing experiences, tangible involvement opportunities and specific types of meaning making related to violence. Implications for models of ally development and for efforts to engage men in antiviolence work are discussed.