While still vastly underrepresented and lagging behind political representation in several other European democracies, more ethnic minorities and immigrants have entered the German Bundestag in 2013 than ever before. This is one of several indicators of Germany's political departure from hegemonic ethnic self-understandings, signaling the nation's complicated, partly still-contested evolution towards political self-conceptions as a “country of immigration.” A significant unanswered question is how and how far this process, which can be conceived as cosmopolitanization, has transformed party politics. This article examines the scope and causes of cosmopolitanization in three dimensions of German party politics after the 2013 Bundestag election: political discourse and programmatic positions on immigration, citizenship, identity, and ethno-cultural diversity; the policy regime of mainstream parties on immigration and the inclusion of ethnic minorities; and the fielding of minority candidates for national public office. It is argued that a belated postethnic cosmopolitanization of German party politics is primarily caused by transformed demographic realities, value change, and new electoral demands. Mainstream political parties—including the center right—have been reluctant but ultimately rational strategic agents reacting to these transformations in the electoral market. Yet, the scope and character of cosmopolitanization also depends on external and internal supply side conditions that enable parties to make programmatic changes, depolarize key issues of the immigration and citizenship policy regime, and recruit ethnic minorities for political representation. In European comparative perspective, the German case may serve as a model for theorizing the cosmopolitanization of party politics.