Despite progress, profound gender inequality prevails and is harmful to the aspirations and well-being of both women and men. While much research has focused on the circumstances that motivate women to engage in collective action to achieve gender equality, more recently, research has identified men’s support for gender equality as a crucial factor for change. In this thesis, we first review the literature on collective action for gender equality, and highlight the role of male allies against gender inequality (Chapter 1). We then review existing measures of (men’s) support for gender equality, and identify a gap in the psychometric literature. In response, we present one pilot study and four main studies developing and validating the comprehensive Support for Gender Equality among Men Scale (SGEMS), comprising a public support for gender equality and a domestic support for gender equality subscale (Chapter 2). Next, we argue that, due to the prescription to avoid everything that is considered feminine, precarious manhood beliefs might function as a barrier impeding men’s conversation about domestic support for gender equality with other men. Across three empirical studies and a meta-analysis of these studies’ results, we show that men endorsing (disagreeing with) precarious manhood beliefs report decreased (increased) levels of domestic support for gender equality in front of an audience of male peers, relative to an anonymous report. Subsequently, across a pilot study and a correlational study, we explore potential underlying motivations for these patterns, and find that feminine stigma concerns and status and employability concerns are related to a decrease in reported levels of domestic support for gender equality. We argue that restrained conversation about domestic support for gender equality slows down masculinity norm change, and hence stifles men’s actual domestic support for gender equality (Chapter 3). Finally, we summarise and integrate the findings across the two empirical chapters, and discuss implications for theory and practice (Chapter 4).