Since 1926, special tax benefits have been available for U.S. citizens working abroad. Internal Revenue Code section 911-which cost an estimated $4.4 billion in 2013- provides a tax exclusion for foreign earned income, as well as an exclusion and deduction for foreign housing costs. GAO was asked to assess section 911. This report (1) describes the number and types of taxpayers using the tax expenditure, and analyzes how the tax expenditure may interact with other provisions of the tax code, such as the foreign tax credit; (2) describes what is known about how the tax expenditure may affect business decisions about the employment of U.S. workers abroad, and U.S. exports; and (3) evaluates the potential advantages and disadvantages of modifying or removing the tax expenditure. To address these objectives, GAO analyzed 2011 IRS statistical data; reviewed the tax code and relevant government and academic literature; and interviewed government officials, experts, and stakeholders, including groups representing citizens working abroad and employers. As its criteria for good tax policy, this report uses GAO's tax expenditures evaluation guide, Tax Expenditures: Background and Evaluation Criteria and Questions, GAO-13-167SP.