This paper considers the tax policy consequences of both real and financial types of international tax avoidance, focusing on U.S. multinational firms over the period 1982–2004. First, income shifting is examined by estimating the relationship between U.S. affiliate profit rates and foreign country tax rates. Second, the effects of taxes on multinational firms’ real operations across countries are considered. Estimates of both financial and real responsiveness to tax rate differences among countries are used to calculate how profits would differ from their current levels absent tax incentives, and thus how U.S. government revenues are affected. Finally, several policy alternatives are discussed.