Large complex infrastructural projects and programs show cost overruns and delays. As these are often funded by governmental bodies, the cost overruns also have an economic impact for society. Where projects are focused on delivering their scope within time and budget, a program is focused on achieving a broader goal. To do so, a program consists of different projects that show interdependencies. This, complemented with many uncertainties and the program's long durations, make programs even more complex than projects. Program management needs to be flexible and able to adjust: adaptivity is a core characteristic of program management. An academic knowledge gap is seen on cooperation strategies that achieve adaptivity in programs. Therefore, this study focused on the identification of success factors for adaptive cooperation in programs. The different research methods have led to the identification of the following factor: mandate and formal structure that together determine the operational framework of teams and organisations. This factor influences the ability to be adaptive by setting rules for the teams. As adaptivity was often associated with social processes, this insight has an academic value and contributes to theory development on adaptivity in program management. In addition to this factor, factors focused on social processes can also influence the adaptivity. Program managers should define the mandate of teams and their formal structure before determining the social acts. This could enable adaptive cooperation in programs and reduce cost overruns and delays. This research provides a starting point for theory development on adaptive program management.