--- - |2 Abstract This paper makes the case for cross‐domain comparison as an undertheorized form of comparative analysis. The units of analysis in such comparisons are not (as in most comparative analysis) predefined units within a domain or system of formally similar yet substantively different categories or entities; they are the domains or systems of categorically organized differences themselves. Focusing on domains of categorical difference that are central to the contemporary politics of difference, we consider two examples of cross‐domain comparison. The first compares sex/gender and race/ethnicity as systems of ascribed identities that are increasingly, yet to differing degrees and in differing ways, open to choice and change. The second compares religion and language as domains of categorically organized cultural difference that are centrally implicated in the politics of cultural pluralism. We situate these cross‐domain comparisons, premised on a logic of ‘different differences’, between generalizing and particularizing approaches to the politics of difference, arguing that these domains are similar enough to make comparison meaningful yet different enough to make comparison interesting. We outline five analytical focal points for cross‐domain comparison: the criteria of membership and belonging, the categorical versus gradational structure of variation within domains of difference, the consolidation or proliferation of categories of difference, the procedures for dealing with mixed or difficult‐to‐classify instances, and the relation between categories of difference and the production and reproduction of inequality. We conclude by considering several potential objections to cross‐domain comparison. - 'The British Journal of Sociology, Volume 70, Issue 4, Page 1135-1158, September 2019. '