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 crossdomain comparison.Political struggles over categorical difference -in the domains of race, ethnicity, nationality, citizenship, indigeneity, religion, language, gender, sexuality, disability, and so on -have become increasingly salient in Western liberal democratic settings. Such struggles are addressed by large bodies of work, much of it implicitly or explicitly comparative. With the significant exception of certain forms of intersectional scholarship, however, comparative work on the politics of difference has been largely restricted to within-domain comparison. 2 We propose that such work can usefully be complemented by cross-domain comparison. Such comparisons can enrich the analysis of the politics of difference by bringing into analytical focus both important cross-domain similarities and key cross-domain differences in matters such as 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.This type of analysis was recently suggested by Floya Anthias (2013), who pointed out that research on different systems of categories can be c...