Tax reforms affect economic performance by changing incentives for business formation, expansion, and operation. The United States has the highest corporate tax rate among countries with advanced economies, and—despite offering significant additional deductions, exclusions, and tax credits—it imposes the heaviest tax burdens. This paper offers a new measure of corporate tax burdens based on information in tax expenditure budgets; this measure implies that the burden of U.S. corporate taxation in 2017 is equivalent to that produced by a corporate tax rate of between 31.7 and 34.8 percent, without additional deductions, exclusions, or tax credits. Efficient design of a business tax system encourages activities with beneficial economic spillovers and imposes lighter burdens on those industries and activities that are most responsive to taxation. Tax reforms have the potential to improve economic efficiency by adjusting the level and design of U.S. business taxes.