United States: Sources

This page lists every source cited on the United States pages of this site, grouped by type. Each entry gives the title, the publisher, the provisions or passages relied on, and the pages that cite it. All sources were accessed on 11 October 2026. Where a source is a web page, the date it was last reviewed or updated is the date shown on that page. Regulation text is taken from the eCFR, which was up to date as of 8 October 2026 when accessed.

Statutes: United States Code

All entries are from the United States Code, 2024 edition, prepared by the Office of the Law Revision Counsel and published by the Government Publishing Office.

• 26 U.S.C. 41, Credit for increasing research activities. Subsections (a), (c)(4)(A) and (d)(2). Cited on Overview and Form 6765 Section G.
• 26 U.S.C. 6001, Notice or regulations requiring records, statements, and special returns. Cited on Claim integrity measures.
• 26 U.S.C. 6109, Identifying numbers. Subsection (a)(4). Cited on Overview and Preparer identification.
• 26 U.S.C. 6212, Notice of deficiency. Subsection (a). Cited on Disputes and appeals.
• 26 U.S.C. 6213, Restrictions applicable to deficiencies; petition to Tax Court. Subsection (a). Cited on Disputes and appeals.
• 26 U.S.C. 6405, Reports of refunds and credits. Subsection (a). Cited on Reviews and audits and AICPA Rule 1.510.
• 26 U.S.C. 6501, Limitations on assessment and collection. Subsection (a). Cited on Reviews and audits.
• 26 U.S.C. 6511, Limitations on credit or refund. Subsection (a). Cited on Reviews and audits, Disputes and appeals and Refund claim requirements.
• 26 U.S.C. 6532, Periods of limitation on suits. Subsection (a)(1), (2) and (4). Cited on Disputes and appeals.
• 26 U.S.C. 6601, Interest on underpayment, nonpayment, or extensions of time for payment, of tax. Subsections (a) and (b)(1). Cited on Penalties.
• 26 U.S.C. 6662, Imposition of accuracy-related penalty on underpayments. Subsections (a), (b), (c) and (d)(1). Cited on Penalties.
• 26 U.S.C. 6664, Definitions and special rules. Subsection (c). Cited on Penalties.
• 26 U.S.C. 6676, Erroneous claim for refund or credit. Subsections (a), (b) and (d). Cited on Overview and Penalties.
• 26 U.S.C. 6694, Understatement of taxpayer's liability by tax return preparer. Subsections (a), (b), (c) and (d). Cited on Overview, Fee rules, Penalties and Disputes and appeals.
• 26 U.S.C. 6695, Other assessable penalties with respect to the preparation of tax returns for other persons. Subsections (b), (c) and (h). Cited on Preparer identification and Penalties.
• 26 U.S.C. 6701, Penalties for aiding and abetting understatement of tax liability. Subsections (a), (b) and (f)(2). Cited on Penalties.
• 26 U.S.C. 7407, Action to enjoin tax return preparers. Subsection (b). Cited on Fee rules and Penalties.
• 26 U.S.C. 7422, Civil actions for refund. Subsection (a). Cited on Disputes and appeals and Refund claim requirements.
• 26 U.S.C. 7602, Examination of books and witnesses. Subsection (a). Cited on Reviews and audits.
• 26 U.S.C. 7701, Definitions. Subsection (a)(36)(A). Cited on Adviser registration and Preparer identification.
• 26 U.S.C. 7803, Commissioner of Internal Revenue; other officials. Subsection (e)(1), (3) and (4). Cited on Disputes and appeals.
• 28 U.S.C. 1346, United States as defendant. Subsection (a)(1). Cited on Disputes and appeals.
• 31 U.S.C. 330, Practice before the Department. Subsections (a) and (c). Cited on Fee rules and Circular 230 section 10.27.

Regulations: Treasury Department Circular No. 230 (31 CFR part 10)

Published by the Treasury Department in the electronic Code of Federal Regulations.

• 31 CFR 10.0, Scope of part. Paragraph (a). Cited on Fee rules and Circular 230 section 10.27.
• 31 CFR 10.2, Definitions. Paragraphs (a)(5) and (a)(6). Cited on Overview, Fee rules, Professional body rules and Circular 230 section 10.27.
• 31 CFR 10.3, Who may practice. Paragraphs (a) to (f). Cited on Overview, Fee rules, Professional body rules, Adviser registration and Circular 230 section 10.27.
• 31 CFR 10.8, Return preparation and application of rules to other individuals. Paragraphs (a) and (c). Cited on Fee rules and Adviser registration.
• 31 CFR 10.27, Fees. Paragraphs (a) to (d) and source note T.D. 9359. Cited on Overview, Fee rules, Professional body rules and Circular 230 section 10.27.
• 31 CFR 10.50, Sanctions. Paragraphs (a) and (c)(1) to (c)(2). Cited on Penalties and Circular 230 section 10.27.
• 31 CFR 10.52, Violations subject to sanction. Paragraph (a). Cited on Penalties and Circular 230 section 10.27.

Regulations: Income tax and procedure (26 CFR)

Published by the Treasury Department and the IRS in the electronic Code of Federal Regulations.

• 26 CFR 1.41-4, Qualified research for expenditures paid or incurred in taxable years ending on or after December 31, 2003. Paragraph (d). Cited on Claim integrity measures, Reviews and audits and Form 6765 Section G.
• 26 CFR 1.6109-2, Tax return preparers furnishing identifying numbers for returns or claims for refund and related requirements. Paragraphs (a)(1) to (a)(3). Cited on Adviser registration and Preparer identification.
• 26 CFR 1.6695-1, Other assessable penalties with respect to the preparation of tax returns for other persons. Paragraph (b)(1). Cited on Preparer identification.
• 26 CFR 301.6402-2, Claims for credit or refund. Paragraphs (b)(1) and (e). Cited on Adviser registration, Preparer identification, Claim integrity measures and Refund claim requirements.
• 26 CFR 301.6402-3, Special rules applicable to income tax. Paragraphs (a)(3) and (a)(5). Cited on Circular 230 section 10.27 and Refund claim requirements.
• 26 CFR 301.7701-15, Tax return preparer. Paragraphs (a), (b)(1), (b)(2)(i) and (b)(3). Cited on Adviser registration and Preparer identification.

Federal Register

• Regulations Governing Practice Before the Internal Revenue Service, notice of proposed rulemaking, 89 FR 104915 (26 December 2024). Treasury Department and Internal Revenue Service. Summary, Dates, Background parts A and B, Explanation of Provisions part B and proposed section 10.51. Cited on Overview, Fee rules, Professional body rules, Adviser registration, Circular 230 section 10.27 and AICPA Rule 1.510.
• Documents associated with RIN 1545-BQ12. Office of the Federal Register. Search result listing one document, the proposed rule of 26 December 2024. Cited on Circular 230 section 10.27.

Court decisions

• Ridgely v. Lew, Civil Action No. 1:12-cv-00565 (CRC), Memorandum Opinion, 16 July 2014. US District Court for the District of Columbia, published by the Government Publishing Office. Pages 1, 3, 7 (note 3), 8 to 10 and 12 to 15. Cited on Overview, Fee rules, Professional body rules and Circular 230 section 10.27.

IRS forms, instructions and publications

Published by the Internal Revenue Service.

• Form 6765, Credit for Increasing Research Activities (Rev. December 2024). Pages 1 to 4, including Sections E, F and G. Cited on Preparer identification, Claim integrity measures and Form 6765 Section G.
• Instructions for Form 6765 (Rev. December 2025). Read in full; in particular What's New, Purpose of Form, Business Component, Sections E and F, "Requirements To Complete Section G", "How To Complete Section G", "Statistical Sampling", columns 49(a) to 56 and "Research Credit Claims on Amended Returns". Cited on Overview, Adviser registration, Preparer identification, Claim integrity measures, Refund claim requirements and Form 6765 Section G.
• Form 1120, US Corporation Income Tax Return (2025). Page 1, "Sign Here" and "Paid Preparer Use Only". Cited on Preparer identification.
• Form 1120-X, Amended US Corporation Income Tax Return (Rev. December 2025). Page 1, "Sign Here" and "Paid Preparer Use Only". Cited on Preparer identification.
• Publication 5, Your Appeal Rights and How to Prepare a Protest if You Disagree (Rev. 4-2021). Pages 1 to 6. Cited on Overview, Adviser registration and Disputes and appeals.

IRS guidance and web pages

Published by the Internal Revenue Service.

• Research credit claims (Section 41) on amended returns frequently asked questions. Page last reviewed or updated 1 October 2026. Introduction and questions 3 to 9, 12 to 18 and 21. Cited on Overview, Preparer identification, Claim integrity measures, Reviews and audits, Disputes and appeals, Refund claim requirements and Form 6765 Section G.
• Required information for a valid research credit claim for refund. Page last reviewed or updated 27 September 2026. Paragraphs 2, 3 and 7. Cited on Reviews and audits and Refund claim requirements.
• Notice 2008-43, Contingent Fees Under Circular 230, Internal Revenue Bulletin 2008-15. Sections "Interim Guidance" and "Effective Date for Interim Guidance". Cited on Circular 230 section 10.27.
• PTIN requirements for tax return preparers. Page last reviewed or updated 16 October 2025. Cited on Adviser registration.
• Understanding tax return preparer credentials and qualifications. Page last reviewed or updated 29 January 2026. Introduction and sections on unlimited representation rights, limited representation rights, Annual Filing Season Program participants and PTIN holders. Cited on Adviser registration, Professional body rules and AICPA Rule 1.510.
• IRS audits. Page last reviewed or updated 17 February 2026. Sections on selection methods, notification, how audits are conducted and records. Cited on Reviews and audits.
• LB&I not currently active campaigns. Page last reviewed or updated 28 September 2026. Entry "Research issues". Cited on Reviews and audits.
• Audit techniques guide: Credit for Increasing Research Activities (i.e. Research Tax Credit) IRC 41, Qualified research activities. Publication date June 2005. Publication note and chapter 5. Cited on Claim integrity measures and Reviews and audits.

IRS Office of Chief Counsel

• Memorandum 20214101F, I.R.C. 41 Research Credit Refund Claims. Dated 17 September 2021, released 15 October 2021. Short Answers 1 to 3, Law and Analysis part A.1 and note 1. Cited on Preparer identification, Disputes and appeals and Refund claim requirements.

Professional body rules

• Code of Professional Conduct (updated for all official releases through September 2026). American Institute of CPAs. ET 0.100.010, 0.100.020, 0.200.020, 0.400 (paragraphs .33 and .45), 1.000.010 (paragraph .14c), 1.510.001, 1.510.005, 1.510.010, 1.510.020 and Appendix C. Cited on Overview, Professional body rules and AICPA Rule 1.510.