The issue of radicalization has drawn significant attention over the last decade, as high-profile mobilizations and far-right violence grow increasingly prevalent in the United States. This has been accompanied by a particular interest in radicalization in the online context, as far-right recruitment and organizing increasingly leverages the affordances of digital platforms. In this dissertation, I advance theoretical understandings of online radicalization processes by analyzing differential participation within one growing and under-examined segment of the far-right: secular male supremacist movements. Based on prior literature identifying increasing extremism in these spaces, and increasing instances of users moving between distinct but related communities, I address two specific research questions: 1) what individual and community-level factors drive differences in engagement in male supremacist communities; and 2) what individual and community-level factors predict user migration to more extreme male supremacist communities?