The study of public opinion polarization is dominated by the US case (Lelkes, 2016; McCarty, 2019). We know less about patterns of ideological polarization in European democracies, and how it varies across ideological domains. Some recent studies have looked at affective polarization (Boxell, Gentzkow and Shapiro, 2020; Reiljan, 2020) but not at ideological polarization in the European context. We aim to explore and document patterns of ideological polarization across European countries from the 1990s until today, by combining a series of comparative public opinion datasets such as the ESS, ISSP and World Values Surveys. Has ideological polarization – operationalised with bimodality (Lelkes 2016) as well as polarity measures – increased in European countries over time? Are ideological polarization patterns different for different policy domains? What underlying cleavages are responsible for rising ideological polarization levels? The study advances the field of political polarization research by not only providing a comparative assessment of ideological polarization trends over-time, but also by focusing on various different cleavages when measuring polarization – thus avoiding focusing on partisanship as the sole basis of the polarity measure. The study offers a detailed assessment of the nature and direction of public opinion polarization in European countries over-time, and represents a crucial resource to explore the causes of political polarization in the European context.