George Yin (Chief of Staff, Joint Committee on Taxation) has published his May 20 speech to the Exempt Organizations Committee of the ABA Tax Section on The Tax Gap in 107 Tax Notes 1449 (June 13, 2005), also available on the Tax Analysts web site as Doc 2005-12322, 2005 TNT 113-37.  Here is the opening:

I would like to talk with you today about the so-called "tax gap," a topic which cuts across several of our current responsibilities. Recent hearings in Congress have focused on this gap, which is the difference between the amount of tax due from legal activities and the amount voluntarily paid by taxpayers in a timely manner, and the Joint Committee staff issued a report earlier this year setting forth a range of options to improve tax compliance. I also think, for reasons I will mention in a moment, that any consideration of major tax reform in this country must give primary consideration to issues of tax compliance and enforcement.