The implementation of IT project governance (ITPG) is a response to the increased regulatory pressure and the high failure rate of IT projects. Although ITPG is common, there is little research on this phenomenon, and very little is known about the forces that drive ITPG or the process by which such governance is implemented in organizations. This paper presents a process theory of ITPG implementation developed from case studies of five large companies in the financial services industry, using the grounded theory method. The model proposes three phases of ITPG implementation: standardization, centralization, and professionalization, and key drivers of each phase. The paper also shows how the proposed process theory is consistent with and can be integrated with institutional theory to demonstrate ITPG as an institutional process.