The aim of this paper was to analyse the role of borders and types of borderlands in cross-border cooperation. Almost 600 projects from seven Interreg IIIA Programmes, in which Polish border regions participated in the years 2004–2006, were examined. The authors paid special attention to the question whether the structure of co-operation fields is uniform or diversified along all borders. Although many similarities did exist, there were also important differences. It turned out that the common legal framework of Interreg Programmes did not guarantee exactly the same realisation of trans-border cooperation. The so called ‘integrating factor’ also played an important role. The type of border and neighbouring country, as well as different local conditions also had an impact on the programmes’ implementation. Therefore, the effectiveness of trans-border programmes depends on their adjustment to specific regional conditions.