Are social movement organizations euro-skeptical, euro-pragmatic or euro-opportunist? Or do they accept the EU as a new level of governance to place pressure on? Do they provide a critical capital, necessary for the political structuring of the EU, or do they disrupt the process of EU integration? These questions are addressed on the basis different sources and methods, with a comparison among different countries as well as an analysis of the historical evolution of the Europeanization of social movements in the last twenty years. The empirical basis includes surveys of activists at international protest events targeting the European Union (for a total of about 5,000 interviews); a discourse analysis of documents and transcripts of debates on European politics and policies conducted during the four European social forums hold between 2002 and 2006 and involving hundreds of social movement organizations and ten thousands of activists from all European countries; about 320 interviews with representatives of civil society organizations in six EU countries (France, Germany, the United Kingdom, the Netherlands, Spain, and Italy); and one non-EU-member state (Switzerland), as well as at EU level; and a systematic claims analysis of the daily press in selected years between 1990 and 2003. The empirical research allows for the observation of different paths of Europeanizations by social movements and civil society organizations. Moreover, it confirms that issues related to the degree and forms of participation of social movement organizations in European politics (and their support toward Europe) emerge as particularly central in the process of creation, together with a European polity, of a democratic polis.