Over the past decade the European Union has been negotiating two preferential trade agreements (PTAs) with respectively Canada and the United States: the Comprehensive Economic and Trade Agreement (CETA) and the Transatlantic Trade and Investment Partnership (TTIP). While CETA negotiations were successfully concluded in August 2014, TTIP negotiations made slow and little progress, and eventually stalled after the 2016 US presidential elections. This work aims at answering the following question: why were CETA negotiations concluded successfully and those of TTIP were not? To do so, the paper is divided into three sections: the first section introduces and describes the object of study – namely TTIP and CETA – underlining relevant similarities and differences between the agreements. In the second and third sections, using a comparative approach, I analyze the aspects that according to available literature might have played a determinant role for either the success or failure of the negotiations. Specifically, the second section is dedicated to domestic politics, while the third discusses major controversial issues present in both negotiating agendas. The results of the analysis are then presented in a dedicated section at the end of the work.