Inter-organizational networks are frequently used to execute large and megaprojects. This study develops a theoretical framework for the governance of these networks. Twenty-eight case studies, each representing a network for a project, were assessed using 124 interviews in ten countries. A three-layer governance model is derived from the analysis. At the lowest layer (network governance) is the individual network of organizations collaborating in a project. This layer is explained through Multi-level Governance Theory. The intermediate layer (governance of networks) addresses the steering of the different networks these organizations are part of, such as for training, certification, safety etc.. At the top layer (metagovernance) are the ground-rules, set by governments or other investors to regulate how the two other layers are allowed to set up their governance. The study’s resulting theory combines three so far separate levels of governance into an overall understanding of large inter-organizational networks for projects. It provides parameters for practitioners to optimize their networks for better project results.