"A regulation is issued by the Internal Revenue Service and Treasury Department to provide guidance for new legislation or to address issues that arise with respect to existing Internal Revenue Code sections. Regulations interpret and give directions on complying with the law." (IRS website)
Final regulations (or rules) are published in the Federal Register and are codified in the Code of Federal Regulations. IRS regulations are mostly found in volume 26 of the CFR.
Final and temporary regulations are "printed . . .[u]nder the heading 'Treasury Decisions' (T.D.) in the Internal Revenue Bulletins (I.R.B.), . . . [and] in the Cumulative Bulletin (C.B.)." (Publication of Regulations, IRM § 22.214.171.124.3.5) Treasury Decisions (either final or temporary regulations) are numbered sequentially.
As per the Bluebook citation quoted below, citations to IRS tax regulations often do not include a reference to the pertinent CFR title (title 26). The CFR title number is replaced with "Treas. Reg."
The following citation resources may be informative.
Below are pertinent abbreviations.
Certain grouping of regulations are informally given names.
Check-the-box regulations, Treas. Reg. § 301.7701-1 et seq.
Below are links to sources offering current regulatory material on tax topics.
Warning: Some of the sources listed below may also contain superseded regulatory material. Researchers should independently verify the currency of any given regulation.
Below are links to sources offering current regulatory material--specifically the Code of Federal Regulations and the Federal Register.
Warning: Some of the sources listed below may also contain superseded regulations. Researchers should independently verify the currency of any given regulation.