Partnerships have a fundamental role in developing innovative, balanced, and affordable programs. They increase the opportunities for scientists across different domains of space science, therefore implying that we get more than the sum of the involved parts. International cooperation in space science can take place in several ways and at different levels, depending on the involvement and responsibilities of the partners, as given by the corresponding task agreements. Cooperation may be established at the level of data sharing, including access to observing time, flight opportunities, the provision of science instruments, the development of joint missions, or programmatic coordination. In this chapter, we will focus on the differences between cooperation models, with particular attention to the management implications.