Many governments seek to attract private finance for infrastructure through public-private partnerships (PPPs) in order to maintain investment at the same time as limiting public spending. Experience with PPPs has, however, been mixed. Some transport PPP projects have delivered major cost savings but many more have exceeded their budgets. PPPs are prone to overestimating revenues and when projects run into financial difficulty, risks have a tendency to revert to the taxpayer. The report examines the nature of risks and uncertainty associated with different types of PPP project and the practical consequences of transferring risks to private partners. It assesses the fiscal impact of PPPs and discusses budget procedures and accounting rules to limit the public liabilities they can create. The report also reviews the relative merits of tolls, availability payments and regulated asset base models for attracting finance for public infrastructure from private investors on a sustainable basis.