Open innovation (OI) is increasingly being adopted by city administrations and municipalities. However, the extent to which the public sector applies OI is yet unclear. Furthermore, studies in OI in public organizations has primarily focused on citizen inclusion and the barriers and drivers of attracting and engaging citizens and seldom considered other external actors, such as academia and other public organizations. Consequently, this study reviews the literature on OI in public organizations and applies the concept of organizational boundary to interpret the relationships among OI actors in the public sector. The review identifies that the maturity of OI in public organizations are low between all actors and these organizations differ to a great extent in terms of which aspects of organizational boundary are open. However, grand challenges and social innovation are exceptions demonstrating a high level of maturity. Furthermore, the use of intermediaries has the potential of opening all aspect of boundaries and hence achieving a high level of success. Finally, the framework presented in this review is used to suggest future research.