Through an analysis of relevant social science evidence, this article provides a deeper understanding of critical mass, a concept that has become central in litigation efforts related to affirmative action admissions policies that seek to further the educational benefits of diversity. We demonstrate that the concept of critical mass requires an understanding of the conditions needed for meaningful interactions and participation among students, given the particular institutional context. To highlight this contextual definition of critical mass and to avoid further obfuscations in the legal debate, we offer the term "dynamic diversity" and outline four main components of dynamic diversity that institutions can attend to. By thinking of dynamic diversity as the goal, institutions and lawyers should be better poised to answer the question of how much diversity is necessary for leveraging its educational benefits.