What is the intersectional thesis a thesis about? Some understand it as a claim about the metaphysics of oppression, social kinds, or experience; about the limits of antidiscrimination law or identity politics; or about the importance of fuzzy sets and multifactor analysis in social science. We argue, however, that intersectionality, interpreted as a thesis in any particular theoretical domain, faces regress problems. We propose that headway on these and other questions can be made when intersectionality is modeled as a regulative ideal, i.e., a guiding methodological and practical principle, and not as a general theory or hypothesis. Qua ideal, intersectionality requires activists and inquirers to treat existing classification schemes as if they are indefinitely mutually informing, with the specific aim of revealing and resisting inequality and injustice. Qua regulative, intersectionality points to a rich and expanding set of heuristics for guiding social-scientific research and the construction of multifaceted political coalitions. A ppeals to intersectionality serve to remind us that social categories like race and gender cannot be adequately understood independently from each other. But what, exactly, is the intersectional thesis a thesis about? Answers to this question are remarkably diverse. Intersectionality is variously understood as a claim about the nature of social kinds, oppression, or experience (Cole 2009;