This dissertation examines the phenomenon of co-ethnic immigration to West Germany and Israel between 1948 and 1992. Its core object of study is the legal and institutional arrangements for co-ethnic immigration in both countries. Transcending notions of “ethnic stateness” and “diaspora return,” this thesis argues that the phenomenon was sustained in each case by specific models of statehood that originated in the wake of the Second World War. It shows that the German “refugee state” and the Israeli “settler and diaspora state” emerged from different contexts of population movement and originally followed fundamentally different logics of co-ethnic immigrant selection. Under the impact of international, Cold War-related developments as well as generational change among the target populations, the German and Israeli models partly converged over time, in particular during the transformation period between the mid-1960s and mid-1970s. Their re-divergence after the end of the Cold War, in turn, was due to the persistence of national differences in the approach to co-ethnic immigration. Germany never became a “national homeland” like Israel that actively sought the “return” of its “diaspora.” This dissertation further deals with the meaning and content of “co-ethnicity” in each case. Going beyond the letter of the respective laws, it takes a practice-oriented approach, analyzing the interpretation of legal definitions of “co-ethnicity” by bureaucratic actors in individual cases. It contends that the interpretation of “co-ethnicity” was largely dependent on the conceptions and agendas of specific gatekeepers who competed for definitional power in the context of co-ethnic immigration control. Furthermore, the thesis argues that the production of co-ethnicity must be understood as a relational process between the country of origin, the country of destination, and possibly a transit country. In the analysis of these processes, “coethnicity” emerges as a complex notion that goes beyond categories of “descent” and “culture,” and can be better described in terms of declaration, performance, intuition, and consensus. The dissertation thus contributes to the study of nationalism, citizenship, immigration control, and the state.