In the late 1970s and the 1980s, a number of radical left political theorists focused their philosophical attention on the relevance of ancient atomism, revitalizing a tradition that went back to Karl Marx's work on his dissertation. This essay looks at the uses of atomism by two thinkers in particular, Jacques Rancière and Alain Badiou, in order to see how their discussions of and references to ancient materialism help to shed light on their fundamental disagreements about the nature of community and equality. First, this paper argues that what Badiou and Rancière most obviously share in their assessments of atomism is a negative judgment regarding the post-swerve constitution of the world, while what most obviously distinguishes their positions is their differing judgments regarding the preswerve rain of the atoms in the void. Becoming clear both about how Badiou and Rancière respond to what comes before and after the atomistic swerve helps to clarify an implicit response on Rancière’s part to what has become Badiou’s chief objection to Rancière’s political theory. Second, this paper argues that the fact that Badiou assesses both what comes before and what comes after the swerve as negative, while Rancière assesses only what comes after the swerve as negative, makes clear that their most essential point of difference concerns the status of the swerve that mediates between before and after. Working through the complexities of Badiou’s analysis of the swerve and uncovering Rancière’s extremely subtle analysis of the swerve helps to clarify a major aspect of what has become Rancière’s chief criticism of Badiou’s conception of philosophy.