Towards a Principal Agent Based Typology of Risks in Public Private Partnerships There is a strong economic rationale for close cooperation between the public and private sectors. This has resulted in a significant increase in the demand for the provision of public services through instruments combining public and private money such as public private partnerships (PPPs or P3s). We describe these arrangements and explore how they can be analyzed using standard tools in economics (incentives and principal agent theory). We discuss the implications of our approach in terms of identifying risks that are often overlooked before turining to the optimal risk sharing between the public and private partners in particular with respect to information asymmetries in risk perceptions. This allows us to propose a typology of the risks associated with PPPs where both internal risks (the risks associated with the contract) and external risks (those associated with the project) are considered