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Every year, thousands of taxpayers and their advisors are required to mail special disclosure forms that reveal details of potentially abusive tax strategies to the Office of Tax Shelter Analysis of the Internal Revenue Service in Ogden, Utah. This mandatory disclosure regime has been widely praised as one of the government’s most effective weapons in its war on tax shelters. In contrast to this largely positive portrayal, however, this Article argues that the current tax shelter disclosure law is incomplete. While the primary aim of current law is to deter nondisclosure of information by taxpayers and advisors, my claim is that the government should also strive to prevent behavior that may be just as problematic to the IRS’s ability to detect and challenge tax shelters—overdisclosure of information. As this Article demonstrates, since the introduction of the tax shelter reporting rules in 2000, taxpayers and advisors have frequently disclosed to the IRS their participation in routine, nonabusive transactions or details of activities that are irrelevant to tax shelter detection. After investigating the sources of overdisclosure, I conclude that the tax law itself invites this response from distinct types of taxpayers and advisors. Conservative types overdisclose out of excessive caution, while aggressive types overdisclose in an attempt to avoid detection of abusive tax planning. As a result of the threats to tax administration posed by overdisclosure, I offer three novel proposals for proactively reducing its occurrence: the introduction of anticipatory angel lists when the IRS designates new listed transactions; the enactment of targeted overdisclosure penalties; and a non-tax documentation requirement for business taxpayers.