This paper synthesizes evidence from Workshop 4 ‘Criteria for successful collaboration’ of the 15th International Conference on Competition and Ownership in Land Passenger Transport. This workshop focused on collaboration between public and private organisations as a key dimension of public transport governance. Collaborative arrangements can in some cases be a complementary approach to owner-instruction relationships (when allowed within the legal framework), overcoming or at least addressing some of the “critical interfaces” and problems that “fall between the cracks” in formal institutional structures. Collaboration between organisations with different resources and aims is often crucial for the ability to identify, develop and implement efficient solutions to problems that exceed traditional divisions of responsibility. It can foster trust (trusting partnerships) and joint capacity for innovation; and it can take place in formalized partnerships or more informal networks.Papers at the workshop addressed both positive and negative experiences of collaboration in Scandinavia, Brasil, Chile, Great Britain, the Netherlands and Australia from an empirical perspective, but several more theoretical papers considered the place of collaboration within wider governance frameworks. The workshop discussions led to a clearer definition of collaboration, and the formulation of key lessons on collaboration as a critical dimension in the interaction between the organisations that drive the development of current public transport operations and management, and future public transport improvements