One of the few advantages of our complex tax code is that the information gathered can, in principle, provide researchers with accurate estimates of wages, investments, retirement savings, and many other economic variables. In practice, however, it is very hard for researchers to gain access to that information. Recognizing the demand for such data, the Internal Revenue Service has begun making more of its information available in aggregated tables and in de-identified compilations known as "Public Use Files." This two-year grant funds a project by the Tax Policy Center (TPC), a joint venture of the Urban Institute and the Brookings Institution, to help make IRS data more useful to researchers, policymakers, and the public. Over the course of the next two years, researchers at the Tax Policy Center propose to add new information to existing IRS data offerings, including data about age, gender, and how joint earnings are split between couples. They will also develop new methodologies for estimating the characteristics of those who do not file taxes, allowing more robust conclusions to be drawn from IRS data. New data and methodologies will be developed and added in ways that protect taxpayer anonymity and privacy.