The Internal Revenue Code (IRC) is Title 26 of the United States Code , and the related regulations are Title 26 of the Code of Federal Regulations. You can find these in print and electronically with all versions of the US Code and Code of Federal Regulations (see "United States Code" and/or "Code of Federal Regulations).
The IRC and related regs are also published as free-standing paperback volumes (from CCH and RIA), as CD-ROMs, and they are included in most online tax databases, including Tax Analysts' Federal Research Library, RIA's CheckPoint and the electronic edition of the CCH Standard Federal Tax Reporter on Intelliconnect.
You can also get the Code and Regs as part of the United States Code and the Code of Federal Regulations, respectively. This is particularly useful because there are reliable, free Internet editions of the USC and CFR (see "United States Code" and "Code of Federal Regulations").
To see if or when a section of the tax code was amended look in the annotations following the text. For recent changes to the tax code, look in the annotations to the text on Lexis or Westlaw, or search a database of Public Laws. For regulations, you could also check the annotations to the text on Lexis or Westlaw, or you could search the Federal Register or look through the List of CFR Sections Affected.
Historical Editions: Some larger law libraries keep volumes of the Code & Regs back many years, and you can find old Codes and Regs in back editions of the USC and CFR (see "United States Code" and "Code of Federal Regulations." Also, there is a multi-volume set called Cumulative Changes in the Internal Revenue Code of 1954 and Tax Regulations Under the Code that covers 1954 through 1985. Westlaw's "Internal Revenue Code of 1954" lets you search the Code as it existed before the Tax Reform Act of 1986 (FTX-IRC-54).
Legislative History: BNA's multi-volume Tax Management: Primary Sources provides legislative history materials for each section of the IRC. In addition, Lexis has a great tax legislative history database (FEDTAX;LEGIS); Westlaw has a legislative history database (LH) for the U.S. Code since 1948, as well as a database just for materials on the Tax Reform Act of 1986 (FTX-TRA86). Checkpoint has selected legislative history materials back to 1990.
Also, Conference Reports and some other documents are published in the IRS's Cumulative Bulletins (see "Internal Revenue Service"). They sometimes come as freebies for subscribers to the multi-volume tax treatises.
If there is one, look at the "Blue Book" and any other report by the staff of the Joint Committee on Taxation to explain major tax laws after they are passed. Blue Books are posted from 1996 on the JCT Web site, and many law libraries keep the old editions published by the GPO and CCH. You can search through old editions of the Blue Book from 1970 on Lexis (FEDTAX;JCTBB) and from 1976 on Westlaw (FTX-JCS).
The House Ways and Means Committee's "Green Book" may also be useful, again, if there is one.
See also "Federal Legislative History."
Public comments on Regs: For recent comments, check Tax Notes Today through the Federal Research Library, Lexis (TAXANA;TNT) or Westlaw (TNT). For comments from 1985-1994, check the Tax Notes CD-ROM. For older comments call the IRS library and see if they can help. If not, you might have to file a FOIA request with the IRS. Call the IRS Reading room for more information (202-622-5164, extension 7).
