This article explores how the concept of minority national-cultural autonomy (NCA) has been defined and practiced in contemporary Estonia, combining data from interviews and previously unanalyzed archival sources to trace debates and policymaking processes back to 1988 and ascertain: why (and for whom) NCA was adopted; the functions ascribed to NCA institutions; and the effectiveness and legitimacy of the model in the eyes of different “noncore” ethnic communities. In so doing, the article uses NCA as a fresh lens for analyzing the more general politics of post-Soviet state and nation-building in the country, situating this case within the “Quadratic Nexus” framework. Estonia’s NCA law is generally viewed as irrelevant to ongoing issues of diversity governance in the country. However, Finnish and Swedish minority autonomies have been established and, in recent years, there have been three applications to establish a Russian NCA. None have been approved, and yet some authors see them as evidence that NCA could (and should) have a role to play in bringing about a more meaningful accommodation of ethnic diversity. Having reviewed the evidence, however, the article concludes that this claim is misplaced.