European Territorial Cooperation programmes (also known as Interreg) are designed to promote integration by encouraging organizations in multiple regions to work together on projects to address shared challenges. While some key aspects of these programmes have been studied (territorial scope, thematic areas, types of initiatives), research into participant organizations and their logic within partnerships (groups of organizations working together on projects) and the reasons for their participation in multiple projects, individually or in clusters, has been less thorough. This article presents a quantitative analysis of programmes under Interreg B and C, investigating the variables that influence organizations' involvement in partnerships and the logic behind repeated collaborations. The aim is to supplement existing research, complementing it and supporting providing a better understanding of this framework to programme planners, enabling them to make more informed decisions when aiming to maximize the impact of their programmes when considering partners and partnerships.