This book presents a comprehensive treatment of the cost-of-capital approach for analyzing the economic impact of tax policy. This approach has provided an intellectual impetus for reforms of capital income taxation in the United States and around the world. The cost of capital and the marginal effective tax rate are combined with estimates of substitution possibilities by businesses and households in analyzing tax and spending programs. This makes it possible to evaluate tax reforms and changes in government spending. Studies of the economic impact of tax policies have taken two forms.