During the 1990's the world saw an unprecedented use of public private partnerships for the delivery of public services. Many of these arrangements have been very successful at improving the efficiency of the delivery of public services. At the same time, the capital market shocks since the late 1990s and over optimistic ex ante projections have caused many of these agreements to either fail or required renegotiation. For other, the returns that the private sector partners received have been far and above what one would normally consider the cost of capital to be for comparable public sector investments. This experience has spurred the demand amongst policy makers for a comparison to be made between the public and private provision of the service to determine the overall value for money of PPP ventures. A central question that must be answered before such a comparison can be made is the appropriate cost of capital or discount rate to use in both of these situations. The papers in this volume address these issues directly and bring the latest views on this topic. The chapters include The Pubic Sector Comparator, and Discount Rates; Time Preference, the Cost of Capital and PPPs; A Reconciliation of Alternative Views on the Social Discount Rate; On Growth, Investment, Capital and the Rate of Return; The New (but old) Approach to the Economic Opportunity Cost of Capital; Risk-A djusted Discount Rates for Public Sector Investments; Social Discount Rates for Canada; The Social Discount Rate for Ontario Government Investment Projects; and The Economic Opportunity Cost of Capital for Canada: An Empirical Update.