Transnational Party Federations (TNPs) have been critical prisms through which to analyse the EU’s tensions between intergovernmentalism and supranationalism. This study focusses on the radical left TNP, the European Left Party (EL), founded in 2004. It centres on four general questions: first; the conditions under which TNPs might be successful; second, how the EL compares to other TNPs, particularly those of the broad centre-left, the Party of European Socialists (PES) and the European Green Party (EGP); third, to what extent the EL has fostered a consensus over positions towards the EU previously conspicuously lacking among the radical left; fourth, the degree to which the EL has enabled an increase in the electoral or policy influence of the radical left in Europe. The study highlights the strengths and weaknesses of TNPs as networks of Europeanisation; they have important roles in the EU political system but remain timid actors with only selectively developed transnationalism.