Following the entry into force of the Treaty of Lisbon on 1st December 2009, territorial cohesion has become a new policy goal of the European Union as well as the economic and social cohesion. But this concept may appear vague and distant. What definition should we give to the territorial cohesion ? How has it become a concern of the Union ? What was the impact in this area of the various European treaties and the role of the European Economic and Social Cohesion Policy ? How can territorial cohesion now be taken into account in EU policies ? These are the questions that this booklet wants to clarify while the European Commission inititiated in October 2008 an extensive debate on this subject with the member States and the socio-economic stakeholders of the Union ?