The importance of cross-border cooperation systems along the external and internal borderlines of the European Union has been increasing since the last enlargements (in 2004 and 2007, 2013). Cross-border cooperation forms gained greater importance in the Hungarian national policy, in the cohesion policy of the European Union as well as in the formation of neighbourhood policy. In the last few years, however, the three most recent crises of the European Union-the 2015 migration crisis, the pandemic and the Russia-Ukraine war-and the socioeconomic impacts of all these crises have resulted in the re-discovery of borders. The European discourse changed fundamentally: instead of the elimination of borders and border obstacles, the issue of security has come to the fore, resulting in reclosing of borders, construction of new borders and application of more stringent border control. The aim of the study is to examine the institution-building process of cross-border territorial cooperation processes in the European Union. Analysing the legal framework for cross-border cooperation established by the Council of Europe and European Union can be recognised as a response to the lack of legal and institutional instruments of cross-border cooperation.