Grassroots groups often find that they need to manage issues of diversity along racial/ethnic, class, gender, religious, and/or citizenship lines, among several other axes of difference. There are strong reasons to expect that diversity is a benefit to such groups, especially in terms of coalition breadth and the widely held expectation that internal heterogeneity helps organizations to resolve collective action dilemmas. Nonetheless, a long tradition within sociological research sets out the expectation that group heterogeneity thwarts the formation of collective identities and group solidarity, and therefore limits the potential for effective organizing. With a particular emphasis on groups active in local community-based organizing since the 1970s, we review studies on a variety of features of group diversity and their effects on mobilizing processes. We find that although researchers remain somewhat divided on these critical issues, the preponderance of evidence suggests that managing diversity poses significant challenges for grassroots organizing efforts. While these challenges may not easily be overcome, we point to a variety of cases in which group differences offered a significant asset to social change efforts.