This report summarizes the literature on the scope and outcomes of P3 projects in the US. It is intended to provide a summary of the state of knowledge of P3s, and serve as a basis for further research. The report discusses motivations for using P3s in transportation infrastructure investment and their advantages and disadvantages. A set of case studies show that most of the advantages identified are evident in project outcomes, while most disadvantages are not. Toll roads are discussed in more detail, and factors that are associated with toll road implementation and outcomes are identified. The report ends with a series of conclusions and their implications for California.