This article explores the Estonian 'integration' project, which was launched in the early 1990s to bridge the differences between ethnic Estonians and ethnic Russians by assimilating the latter with the former. Since the project will soon turn thirty, it is timely to ask whether it has been a success. This article employs Grigorii Golosov's index of political party nationalization to understand whether the 'integration' project has helped to narrow the ideological divide between ethnic Estonians and ethnic Russians. In other words, the study asks whether ethnic Estonians and ethnic Russians vote for the same political parties in comparable proportions or there are 'Estonian' and 'Russian' parties in the country. The analysis of the outcomes of four local and four parliamentary elections that took place in Estonia in 2005-2019 shows that by the mid-2000s Estonia achieved a considerable level of political party system nationalization at both national and local levels. At the national level, political party system nationalization remained high in 2007-2019 despite significant changes in the country's political party system. At the local level, however, political party system nationalization has been diminishing since 2013, leading one to conclude that the Estonian 'integration' project has failed to close the ideological divide between ethnic Estonians and ethnic Russians.