The IRS describes its common types of guidance (Regulation, Revenue Ruling, Revenue Procedure, Private Letter Ruling, Technical Advice Memorandum, Notice and Announcement) at Understanding IRS Guidance - A Brief Primer.
The IRS publishes Revenue Rulings, Revenue Procedures, Notices and Announcements in its Internal Revenue Bulletin/Cumulative Bulletin. It provides taxpayer-specific rulings and determinations (Private Letter Rulings and Determination Letters), Technical Advice Memoranda and Chief Counsel Advice material prepared by the IRS Office of Chief Counsel at its Written Determinations page.
Recommendation for new tax researchers: to understand the value of these IRS materials as authority, read pp. 10-11 (Treasury Regulations) and 22-26 (Agency Decisions and Materials) in Christopher C. Dykes, Federal Income Tax Law: A Legal Research Guide (2nd ed. 2021).
Westlaw: Tax Administrative Decisions & Guidance provides searchable collections of IRS Revenue Rulings, Revenue Procedures and Private Letter Rulings.
KeyCite Tip: Thomson Reuters notes that KeyCite also is available for regulations and administrative decisions. This helpful YouTube video: Mary Whisner, Gallagher Law Library, Westlaw for Tax Research: KeyCite (Nov. 3, 2020) discusses KeyCiting a Revenue Ruling.
IRS, Understanding IRS Guidance: A Brief Primer states: "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 are published in the Federal Register. Generally, regulations are first published in proposed form in a Notice of Proposed Rulemaking (NPRM). After public input is fully considered through written comments and even a public hearing, a final regulation or a temporary regulation is published as a Treasury Decision (TD), again, in the Federal Register."
Free Source:
Federal Register (1936-) (Also available in Westlaw, Lexis and HeinOnline.)
Code of Federal Regulations = the codified source of temporary and final regulations.
Free Source:
Code of Federal Regulations (annual editions from 1996-) (Also available in Westlaw, Lexis and HeinOnline.)
According to IRS, Tax Code, Regulations and Official Guidance, Treasury Regulations appear in 26 Code of Federal Regulations.
Westlaw: Tax Regulations includes Title 31 - Part 10 - Practice before the IRS (Circular 230) + Title 26 - Internal Revenue - Treasury Regulations
Checkpoint Edge provides a template to retrieve final, temporary and proposed Treasury Regulations (published by RIA) by citation.
VitalLaw: Tax: Federal home page > Primary Sources pull-down menu: Laws & Regulations > Federal Tax Regulations. Tax: Federal home page also offers an Advanced Search feature that allows researchers to search within Select Content: Federal Tax Regulations.
Print Source:
Code of Federal Regulations [KF70 .A3, National collection]
IRS, Understanding IRS Guidance: A Brief Primer states: "[a] revenue ruling is an official interpretation by the IRS of the Internal Revenue Code, related statutes, tax treaties and regulations. It is the conclusion of the IRS on how the law is applied to a specific set of facts."
Free Source:
Treasury Dep't., IRS, Internal Revenue Bulletin (1995-)
Other Sources:
Treasury Dep't., IRS, Cumulative Bulletin, available in HeinOnline (1919-2008 + Weekly Bulletin Cumulation for recent years), LLMC Digital (1922-2008)
Lexis: Advanced Search: IRS Cumulative Bulletin and Internal Revenue Bulletin (1954-)
Checkpoint Edge provides a template to retrieve Revenue Rulings (published by RIA) by citation. BLS students, faculty and administrators: see bottom of this Checkpoint Edge guide box for instructions to create Checkpoint Edge individual accounts.
VitalLaw: Tax: Federal home page > Primary Sources pull-down menu: IRS Administrative Rulings & Positions > Revenue Rulings
VitalLaw: Standard Federal Tax Reporter (2024) also provides recent Revenue Rulings in Table of Contents section: 2024 Rulings.
IRS, Understanding IRS Guidance: A Brief Primer states: "[a] revenue procedure is an official statement of a procedure that affects the rights or duties of taxpayers or other members of the public under the Internal Revenue Code, related statutes, tax treaties and regulations and that should be a matter of public knowledge."
Free Source:
Treasury Dep't., IRS, Internal Revenue Bulletin (1995-)
Other Sources:
Treasury Dep't., IRS, Cumulative Bulletin, available in HeinOnline (1919-2008 + Weekly Bulletin Cumulation for recent years), LLMC Digital (1922-2008)
Lexis: Advanced Search: IRS Cumulative Bulletin and Internal Revenue Bulletin (1954-)
Westlaw: IRS Revenue Procedures (1955-)
Checkpoint Edge provides a template to retrieve Revenue Procedures by citation. BLS students, faculty and administrators: see bottom of this Checkpoint Edge guide box for instructions to create Checkpoint Edge individual accounts.
VitalLaw: Tax: Federal home page > Primary Sources pull-down menu: IRS Administrative Rulings & Positions > Revenue Procedures
VitalLaw: Standard Federal Tax Reporter (2024) also provides recent Revenue Procedures in Table of Contents section: 2024 Rulings.
IRS, Understanding IRS Guidance: A Brief Primer states: "[a] private letter ruling, or PLR, is a written statement issued to a taxpayer that interprets and applies tax laws to the taxpayer's specific set of facts." The IRS notes: "[a] PLR may not be relied on as precedent by other taxpayers or IRS personnel."
Treasury Dep't., IRS, Written Determinations provides taxpayer-specific rulings and determinations (Private Letter Rulings and Determination Letters), Technical Advice Memoranda and Chief Counsel Advice material.
Other Sources:
Westlaw:
Checkpoint Edge provides a template to retrieve Private Letter Rulings, Technical Advice Memoranda and General Counsel Memoranda (RIA) by citation.
VitalLaw: Standard Federal Tax Reporter (2024) provides recent Letter Rulings and Chief Counsel Advice in Table of Contents link: 2024 Letter Rulings.