This guide provides a brief outline of the neoclassical theory of the public sector to put into context the reason for deriving shadow prices and to help the reader understand what it is that a government should be trying to do when it "intervenes" in the economy by planning a project. It describes experiences of the World Bank and other organizations in applying project economic analysis in developing countries. Developments in the use and interpretation of "willingness to pay" analysis and "foreign exchange numeraires" are discussed in some detail. It also discusses cost-benefit analysis in terms of the strategic planning model. The problems caused by inflation - both domestic and foreign - are reviewed in some detail, and suggestions are made for dealing with its impacts. Additional recommendations on setting up project accounts are presented. Exchange rate forecasting is addressed in terms of the "purchasing power parity" model of trade theory - the most widely used model for forecasting exchange rates in project appraisals. The issue of the discount rate for project economic analysis is also taken up. Finally, this guide presents many concrete examples of economic valuation problems faced by World Bank analysis in recent years. The examples cover a wide range of countries and valuation issues.