Tax Research - Federal Guide

This guide on federal tax research explains where and how to find tax materials.

Treasury Regulations

Regulations are the highest administrative authority issued by the Treasury Department. They are published in the Federal Register and codified in Title 26 of the Code of Federal Regulations (C.F.R.). Title 26 of the C.F.R. is updated annually on April 1, and the researcher should be sure to consult the most current version of the regulation.

Citations. Unlike other regulations which are cited to the Code of Federal Regulations, Treasury Regulations are not cited to the C.F.R. and are cited as, for example, Treas. Reg. §1.72-16(a) (1963). For more information, see Bluebook T1.

Treasury Regulations have a very organized numbering system. For example, Treas. Reg. § 20.7520-2(b)(3) indicates that this regulation is located in Title 26 of the C.F.R., part 20. The regulation relates to Internal Revenue Code § 7520. This citation is to subsection 2(b)(3) of the regulation.

However, note that the number after the decimal point in Treas. Reg. § 601.xxxx, pertaining to I.R.S. procedural rules, does not correspond to sections of the Internal Revenue Code.

Related regulations. A section of the Internal Revenue Code may have related Treasury Regulations in several different parts of Title 26 of the C.F.R.

The most commonly-seen parts of Title 26 of the C.F.R. are listed below.

1 Income Tax
20 Estate Tax
25 Gift Tax
29 Generation-Skipping Tax
31 Employment Tax
301 Procedure & Administration
601 Commissioner's Rules

For example, Internal Revenue Code § 7520 (Valuation tables for annuities) has the following related regulations:

  • Treas. Reg. § 1.7520-1 (regulation relating to the tables' use in income tax)
  • Treas. Reg. § 20.7520-1 (regulation relating to the tables' use in estate tax)
  • Treas. Reg. § 25.7520-1 (regulation relating to the tables' use in gift tax)

A Treasury Regulation may have a subsection -0. This subsection is often a table of contents or an introduction to a series of related regulations.

Treasury Decision number. A Treasury Regulation also has a Treasury Decision (T.D.) number. This number is chronologically-assigned. Specialized tax databases may use the T.D. number rather than the Treasury Regulation citation.

Current Version

Historical Versions


When a regulation is promulgated, a preamble explaining the regulation is published in the Federal Register. To find a preamble, you need to identify the relevant Federal Register citation. 

On Lexis and Westlaw, the Federal Register citation is located in the "Credits" or "History" note below the text of the regulation.

On Checkpoint, the preamble can be obtained by clicking on the Treasury Decision credits at the end of the regulation.

Additional Resources for Preambles:

  • Bloomberg Law: Tax
    • ​​Federal > Statutes & Regulations > Treasury Decision Preambles.
  • Lexis Tax
    • Federal > Search Regulations > Proposed Regulations & Treasury Decisions. Includes preambles for proposed treasury regulations. 

  • Tax Notes Research

    • Freely available resource for Treasury Decisions, including preambles.

Related Research Guides

Specialized Tax Databases

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