Microbicides were designed to give women an HIV prevention tool that they could use without a male partner’s involvement. However, research suggests that male partner approval or support is often desired, or even required, for women’s microbicide use. Indeed, participants in microbicide studies have described a continuum of male partner engagement in product use. For some women, microbicide use improved communication with partners, reinforcing product adherence. For others, it increased the risk of social harms, including intimate partner violence (IPV), because partners considered microbicide use a threat to their own power. As trials of promising microbicide candidates near completion, it is important to identify, measure, and address the ways in which gender norms and power differentials within relationships affect women’s ability to access and consistently use microbicides.