The subject of the research project is the politicization of European issues in the context of European integration. In particular the research project deals with the following question: Do national parties today mobilize – if yes under which conditions and how – on EU integration and thereby foster the politicization of EU integration? Politicization hereby means a process of public debate about political issues that is in particular carried out in the media. To understand the role of national parties for the politicization we distinguish between issue entrepreneurs (parties on the left and right of the political spectrum) and issue traditionalists (mainstream parties). Considering a three-step model of issues’ politicization process we analyze in the first step the strategic party communication of issue entrepreneurs and address the following research question: (1) Under which conditions do potential issue entrepreneurs decide to put issues regarding Europe on the agenda (salience) and to publicly voice their positions, and which cleavages do they base their arguments on? In the second step we examine in how far their strategic party behaviour affects the overall party agenda and the mass media agenda with the following question: (2) How effective are issue entrepreneurs in affecting the relevant issue environments, i.e. the overall party agenda and the media agenda within a country? In the third step we are interested whether these agenda changes put pressure on issue traditionalists and question: (3) How do issue traditionalists react to changes in the relevant issue environments?