Résumé : The negotiations of the Transatlantic Trade and Investment Partnership (TTIP) triggered an unprecedented level of protests in the European Union (EU) in several member states. However, it was unclear whether the contestation of TTIP led to the Europeanisation of the national public spheres (Risse, 2010), given the general national fragmentation of the political debate in Europe (Koopmans and Statham, 2010a). This thesis analyses the debate and politicisation of TTIP in the Spanish, French and British media, and aims to answer two research questions. First, how and to what extent were national media discourses about TTIP Europeanised? Second, how does this type of Europeanisation of public spheres contribute to the democratic legitimacy of the EU? In order to answer the two research questions, an interdisciplinary theoretical framework has been put forward. Departing from the literature on the European public sphere (Koopmans & Erbe, 2004; Fossum & Schlesinger, 2007; Eriksen, 2005; Trenz, 2009) and the importance of analysing the Europeanisation of public spheres at the national level (Risse, 2010), the thesis argues that the literature often overlooks the role of conflict in the understanding of the public sphere. The gap in the literature has been addressed through a hybrid conceptualisation of the public sphere, combining a typically Habermasian deliberative approach with Chantal Mouffe’s ‘agonistics’. Empirically, the thesis undertakes a framing analysis of two different data sets through both qualitative and quantitative methods. The first data set is composed of press releases of a diverse group of EU-level political actors, in order to see what is the preferred framing of TTIP by different actors. The second is composed of the written articles dedicated to the TTIP negotiations in nine national news outlets (three from each selected country) in France, Spain and the UK, from the public announcement of the negotiations (February 2013) until the negotiations were officially frozen (November 2016). The actors’ discourse has been developed as a frame-mapping exercise undertaken inductively, identifying how different actors made sense of TTIP and put forward a number of competing frames. The findings of the empirical analysis of actors’ press releases indicate the attempt to strategically politicise or depoliticise the discussions around the TTIP negotiations, framed through different values by the different actors. These frames have been situated in categories, depending on whether they depoliticise TTIP, they challenge it in an agonistic or antagonistic way, or they focus on the negotiations as a process. The framing analysis of the media content on TTIP in the Spanish, French and British public spheres has revealed two separate chronological periods in the TTIP debate based on the presence of frames, measured through a framing ratio. The first period represents the traditional ‘permissive consensus’, while the second illustrates the agonistic politicisation of TTIP. Each national public sphere developed its own dynamics, which shows the importance that the national context has when discussing TTIP and Europe (Diez Medrano, 2003). However, while the Spanish, French and British public spheres have slightly different chronologies in their transitions from the first to the second period, there is a transnational coherence in terms of the frames of reference across the three countries. The findings of the media content analysis, particularly during the second period of the TTIP debate in the three countries, support the argument that there has been a Europeanisation of national public spheres that has happened in combination with a value-based and agonistic (Mouffe, 2013) politicisation. Rather than opposing the EU as a polity, the agonistic politicisation that has taken place in the case of TTIP has legitimised the EU by opening a space for the contestation of the negotiations, while accepting the EU as a political arena. The thesis argues that this agonistic Europeanisation of the national public spheres can lead towards an ‘empowering dissensus’ for European integration. The combination of agonistic politicisation and Europeanisation of public spheres is a process that matches ‘policy with politics’ at the EU level and normalises the EU as a polity by channeling conflict as politics in the Union rather than politics of the Union.