The foreign share of the worldwide income of U.S. multinational corporations (MNCs) has risen sharply in recent years. Data from a panel of 754 large MNCs indicate that the MNC foreign income share increased by 14 percentage points from 1996 to 2004. The differential between a company's U.S. and foreign effective tax rates exerts a significant effect on the share of its income abroad, largely through changes in foreign and domestic profit margins rather than a shift in sales. U.S.-foreign tax differentials are estimated to have raised the foreign share of MNC worldwide income by about 12...