This article analyzes how institutions influence the process of identity formation within the Polish minority communities in Belarus and Lithuania. We focus on ways that the identities of people who consider themselves Poles in Belarus and Lithuania are targeted by institutions like the state, schools, and nongovernmental organizations. We aim to shed light on how these processes are shaped by institutional settings and broader political contexts. The authors take a bottom-up approach to institutions and look at how members of the Polish communities in the two neighboring countries conceptualize the role of various institutions—NGOs, schools, Karta Polaka (the Polish Card)—to shape their sense of ethnic belonging. The article is built on a cross-case analysis. Data for the Lithuanian and Belarusian cases, consisting of interviews and secondary sources, were collected independently and then reread in light of a common research question. Through our analysis, we show differences and similarities in how analogous institutions function on the two sides of the border and elaborate on the reasons why these differences occur and what role state policy and supranational regulations play in the process.