Social movements increasingly mobilize contestation either against the institutionalization of the EU system of governance or against the penetration of European norms at the domestic level. As a French association created in 1998 to promote the Tobin tax and to regulate the globalization of financial markets, Attac is a paradigmatic example of social movements intends to “politicize” European issues from below. This chapter uses the methodologies of process-tracing and content analysis applied to the policy programmes of four Attac federations in order to show the development of a “new left” discourse on European integration. Attac has constantly included European debates in its policy statements since 2001, creating national federations while trying to promote a new type of “Euro-protests” against the Bolkenstein directive or the European Constitution. Exercising centrifugal pressures on social-democratic parties in Western Europe, it has obliged some centre-left parties to assume a new discourse around the overarching idea of a “social Europe”.