Third-party development is increasingly relevant for software platform owners seeking to generate complementary assets in the form of applications. The governance of such development involves two seemingly conflicting goals: the maintenance of platform control and the transfer of design capability to users. A key element in simultaneously accommodating these goals is platform boundary resources. However, so far, there is a dearth of theoretical accounts of the role of boundary resources and the process by which such resources can be used to govern third-party development. Drawing on case study research of Apple’s iPhone developer program, we synthesize boundary objects theory and innovation networks literature to develop a process perspective of third-party development governance through boundary resources. In doing this, our research extends and complements existing governance literature and contributes new knowledge about an alternative form of system development.