Internal Revenue Code
Federal tax law begins with the Internal Revenue Code (IRC), enacted by Congress in Title 26 of the United States Code (26 U.S.C.). This version may not be current so check to be sure you are reading the most recent Code.
Treasury (Tax) Regulations
Treasury regulations (26 C.F.R.)–commonly referred to as Federal tax regulations— pick up where the Internal Revenue Code (IRC) leaves off by providing the official interpretation of the IRC by the U.S. Department of the Treasury.
Other Official Tax Guidance
In addition to participating in the promulgation of Treasury (Tax) Regulations, the IRS publishes a regular series of other forms of official tax guidance, including revenue rulings, revenue procedures, notices, and announcements. See Understanding IRS Guidance – A Brief Primer for more information about official IRS guidance versus non-precedential rulings or advice.
The authoritative instrument for the distribution of all forms of official IRS tax guidance is the Internal Revenue Bulletin (IRB), a weekly collection of these and other items of general interest to the tax professional community.