This is a starting point for understanding some of the basic guidance issued by the IRS.
Internal Revenue Bulletins
The Internal Revenue Bulletin (IRB) is the authoritative instrument of the IRS for announcing all substantive rulings necessary to promote a uniform application of tax law. Issues after June 2003 are available in both HTML and PDF formats; earlier issues are in PDF only.
The IRS sometimes releases Rulings, Procedures and other technical items in advance of publishing them in the Internal Revenue Bulletin. The full text of these advance notices is available in PDF format. This list’s filenames are based on the items’ designations — for example, Announcement 2003-40 is “a-03-40,” Notice 2003-30 is “n-03-30,” Revenue Procedure 2003-50 is "rp-03-50” and Revenue Ruling 2003-60 is "rr-03-60."
In addition to the regulations that interpret the tax laws, there are links to various technical resources.
The codified collection of U.S. laws on income, estate and gift, employment and excise taxes, plus administrative and procedural provisions.
Rulings or determinations issued by the IRS, including Technical Advice Memoranda and Chief Counsel Advice. Sorted by most recent publication number, the listing may also be sorted by Uniform Issue List codes.
A collection of links to published guidance, rulings, administrative manuals and other items.