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Federal Tax Research


 Primary sources contain the law created by one of the branches of government:

Branch Type Source
Legislative Statutory

Internal Revenue Code
Other Federal Statutes
International Tax Treaties
U.S. Constitution

Executive Administrative/

Treasury Regulations
IRS Administrative Documents (Rulings, Procedures, etc.)

Judicial Case Law

Federal Cases from:
     Supreme Court
     Circuit Courts of Appeals
     District Courts
     Court of Federal Claims
     United States Tax Court

Tax Databases

For a detailed description see the Tax Research Databases tab.


Internal Rev. Code

Print Sources:

Treas. Regulations

Print Sources:

Legislation (Library of Congress):  Provides access to bills, resolutions, activity in Congress, the Congressional Record, schedules, calendars, committee information, presidential nominations, treaties and more.

Legislative History

The legislative histories of many federal tax laws are already compiled and available in the following sources online:

For legislative histories in print, see the box on the left.

Tax Citation

Color coded tax citation - statute & regulation


The Internal Revenue Code, found in Title 26 of the United States Code, is the key statutory source for federal tax law.  The Internal Revenue Code is divided into subtitles, chapters, subchapters, parts, and sections.  When citing the Internal Revenue Code, it is standard practice to cite to the "section," which is abbreviated with a section symbol (§).  Sections, in turn, are broken down further, into subsections, paragraphs, subparagraphs, and clauses.  You need to understand this organization to properly interpret the language of the Code.

Other statutory sources include tax treaties, which are agreements countries make to eliminate or reduce double taxation.  Finally, other federal statutes not codified in the Internal Revenue Code may also contain the relevant rules.  For example, some provisions of ERISA (the Employee Retirement Income Security Act, P.L. 93-406) have tax consequences but are not found in the Internal Revenue Code.


Treasury Regulations are the official interpretation of the Internal Revenue Code by the Treasury Department.  Regulations are published in the Federal Register when they are issued, and then printed in the Internal Revenue Bulletin (IRB) the week that they are issued.  The Internal Revenue Bulletin used to be consolidated into the Cumulative Bulletin (CB) on a semiannual basis, but the CB ceased publication in 2008.  The regulations are ultimately codified into Title 26 of the Code of Federal Regulations (CFR).

The numbering of the Treasury Regulations closely follows the numbering of the Internal Revenue Code, except with the addition of a prefix before the Code section number and a suffix identifying the regulation.  The prefix number (e.g., 1.xx) identifies the citation as a regulation, and also signals the type of tax involved (for example, 1 is income tax, 20 is estate tax, 25 is gift tax, 301 is for procedural matters, and so on).

Aside from the regulations, agency documents are also an important administrative source of federal tax law.  These include revenue rulings, which explain how the law applies to a specific factual scenario, revenue procedures, which explain the internal practices and procedures of the IRS, and letter rulings, which describe how the IRS will treat a future transaction, and are applicable only to the taxpayer who asks for the ruling.  There are several other types of agency documents, but these are some of the key ones.


    A taxpayer disputing an IRS finding of additional tax liability may initiate an action in the U.S. Tax Court.  A taxpayer who has already paid a disputed tax and seeks a refund may file a claim in the U.S. District Court or the U.S. Claims Court.  Decisions are appealed to the federal appellate court (in the case of claims court decisions, appeal is to the U.S. Court of Appeals for the Federal Circuit) and then to the Supreme Court.  U.S. Tax Court decisions are either regular decisions or memorandum decisions (the latter usually do not involve an interpretation of the Code).

    Court Reported Binding Upon
    Supreme Court Supreme Court Reporter
    US Tax Cases
    Parties and as precedent for all courts
    Courts of Appeals Federal Reporter
    US Tax Cases
    Parties and as precedent for all courts in that circuit including cases before Tax Court
    District Court/Court of Claims Federal Supplement
    US Tax Cases
    Parties and as precedent for that district (including Tax Court)
    Tax Court Tax Court Reports
    Tax Court Memo
    Parties and as precedent in Tax Court (unless other Fed. Court decided).  Tax Court Reports are cases of first impression.  Tax Court Memo for cases where the issue is how to apply settled law.


    Source:  Paul Callister, Federal Tax Hierarchies & Transactional Law Research, available here.