As immigrant diversity increases across most developed democracies, there is an increasing concern that perceived threats to mainstream interests (both cultural and economic) will produce an ethnocentric response. This study approaches the question using survey measures that explicitly tap respondents' normative conception of membership in the national community. Based on cross-sectional and over-time analysis of the ISSP's “National Identity Module,” it shows that more immigrant-exclusive definitions of the national ingroup are linked to both contextual and individual measures of cultural threat. Perceived economic threat at the individual level is also powerfully linked to this outcome, but contextual measures of economic prosperity are not. This finding lends weight to the argument that increasing levels of immigrant diversity are a threat to an inclusive sense of national identity that includes both natives and immigrants.