Not everyone complies with the United States Internal Revenue Code. Many individuals and organizations fail to file timely tax returns, assess their tax liability correctly, or pay taxes when due. To improve compliance, tax administrators must choose among alternative strategies, such as increasing evaders' risks of punishment, motivating social norms, and making compliance easier. Concerned with these choices, the IRS asked the National Academy to assess previous research on the determinants of taxpayer compliance and to highlight the most promising areas for future research. The Academy's panel authored the two-volume Taxpayer Compliance. Volume I presents the panel's report, which critically reviews previous research on the subject, reaches conclusions about the findings, and recommends future research programs to fill gaps in knowledge. The report also recommends ways to maintain and develop the intellectual, financial, and data resources devoted to taxpayer compliance research.