Organizational learning, in terms of both explorative learning within projects and exploitative learning across projects, is of strategic importance for project-based organizations (PBOs) in industries involving production of complex product systems (CoPS). In this conceptual article, we discuss and reflect on how organizational learning may be addressed in PBOs by the establishment of formal knowledge governance mechanisms in a project management office (PMO). Prior literature on PMOs has discussed a broad and diverse range of PMO functions, without conceptually reflecting on their interdependencies. Here, we synthesize the literature into seven main functions. From an organizational learning perspective, we identify significant synergies among the functions of Developing and maintaining a lessonslearnt database, Developing and maintaining project management standards and methods, Consulting and education, and Strategic management. We reflect on how a PBO may establish a centralized PMO utilizing these four systemic learning-related functions as knowledge governance mechanisms, in order to facilitate explorative and exploitative learning through articulation and codification of knowledge. There are also synergies among the three remaining functions, project resource management, monitoring and control, and project portfolio management. These three functions are, however, control related and could be detrimental to place within a centralized PMO focusing on organizational learning.Keywords: Exploration and exploitation, organizational learning, project-based organizations managing both explorative intra-project learning and exploitative inter-project learning (e.g. Keegan and Turner, 2001;Brady and Davies, 2004) and it is on this literature that this article seeks to build.The challenge of managing exploration and exploitation is particularly relevant in PBOs involved in production of complex product systems (CoPS), such as offshore oil platforms, aeroplanes, shipbuilding, IT and mobile telephone systems, and large building and civil engineering projects (Hobday, 2000;Prencipe and Tell, 2001). In CoPS industries, innovation and explorative intra-project learning are critical aspects for developing and delivering complex and customized products that satisfy evolving customer demands. At the same time, exploitative inter-project learning is necessary to achieve efficient use of limited project resources. These kinds of projects, however, involve highly time-bound social interaction, discrete forms of non-repeatable activity, formal objectives and one-off tasks. They, thus, typically lack the strong ties, continued participation and common identities that characterize the communitybuilding effects found in localized, ongoing, and more routine work activities. Accordingly, project members often lack motivation for a retrospective analysis of their past experiences (von Zedtwitz, 2001), and have little incentive to transfer project learning to the parent organization (Swan et al., 2010; Javer-nick -Will, 2011). Indeed,...