In academic debates surrounding the concept of differentiated integration (DI) it is a matter of utmost importance to understand the regional heterogeneity of preferences toward DI. Poland, Hungary, the Czech Republic and Slovakia, in diplomatic terms known as the Visegrad Group, or V4, used to be the frontrunners of democratic transformation in Central and Eastern Europe. More recently, however, their attitudes toward various aspects of European integration underlined heterogeneity of the enlarged EU. But while as in diplomatic terms the Visegrad Group seems to build a block in many contemporary EU debates, can we observe a similar set of dynamics in these countries related to party politics and DI? The major issue that requires explanation today concerns the drivers of national positions toward DI, and in relation to this paper, the role of political parties. Given the growing extent to which mass party politics matters for the outcome of European integration (as depicted by post-functionalism), and because of the limited academic efforts to study party positions toward DI so far, this paper aims to characterise and explain party positions toward the concept, mechanisms and instances of differentiated integration. Our goal is to situate the case of the V4 in a comparative regional perspective and answer two major research questions: How salient is DI for political parties? How heterogeneous are party positions toward DI and how to explain it? We do so primarily by engaging in the original data collection covering major political parties in the Visegrad Group since 2004.
