Most tax laws can be found in Title 26 of the United States Code (U.S.C.). While other U.S.C. titles are generally referred to by their title number, Title 26 is referred to as the Internal Revenue Code (I.R.C.), or sometimes simply, the Code.
There are free digital versions of the I.R.C. on the IRS and US Government Publishing Office sites, and at Cornell's Legal Information Institute.
Annotated versions of the I.R.C. are particularly useful to researchers because they provide explanations of Code sections and can lead to related regulatory materials, cases, and other resources. Annotated versions of the Code are available on Bloomberg Law, Checkpoint, Cheetah, Westlaw, and Lexis Advance
Print versions of the I.R.C. from 1954 to 2016 are available in USF's Zief Law Library on the top floor at KF 6276 .526 .A19 U54.
When statutory ambiguity arises in the interpretation of an IRC section, courts will look to the legislative history to help determine legislative intent. Thus, it is sometimes necessary to do legislative history research for an IRC section.
For a detailed guide to legislative history research for federal statutes (including tax statutes), see USF's Federal Legislative History Research Guide.
Compiled legislative histories for some federal statutes are available on Proquest Legislative Insight and HeinOnline's U.S. Federal Legislative History Library. Free, publicly available legislative history documents are available via Congress.gov.
If you look up a particular IRC section on either Intelliconnect (CCH) or Checkpoint (RIA), both databases will provide links to Committee Reports (although not necessarily other legislative history documents) for that Code section.
Congress enacted the current IRC in 1986 and has amended it many times since then. The version of the Code that was in effect at the time the relevant event took place governs a particular tax issue, so researchers may sometimes need to consult archived versions of the IRC.
Archived IRC sections are available on Checkpoint (from the Search tab, under "Archives"), Bloomberg Law's Tax Practice Center , CCH's Intelliconnect (under "Federal Tax Primary Sources"), and other commercial tax research databases.
Free, publicly available archived code sections are available on on the US Government Publishing Office's GovInfo online service.
The Joint Committee on Taxation is a nonpartisan committee that assists members of both houses of Congress with tax legislation and writes explanations of tax legislation. While these explanations are written after enactment and therefore are not part of the legislative history per se, the Joint Comittee's analyses can be very helpful for explaining and tracing the path of legislation through Congress and giving the researcher an overview of adopted legislation.
The Joint Committee also publishes a derivation table to help researchers reconcile the difference in the numbering schemes between the 1939 and 1954 enactments of the Internal Revenue Code. This is useful because the numbering system for the original 1939 enactment of the Internal Revenue Code was very different from the numbering schemes used in the two later major enactments - in 1954 and 1986 (the current Code).
The Bluebook has special citation formats for tax materials. For Internal Revenue Code citations, see R 12.9 (20th ed. p. 129). For example, section 61 of the Internal Revenue Code would be cited I.R.C. § 61 (2012).