Internal Revenue Service website for charities and nonprofit entities: http://www.irs.gov/charities/index.html
Publication 557: Tax-Exempt Status for Your Organization: http://www.irs.gov/pub/irs-pdf/p557.pdf
Form 1023: Application for Recognition of Exemption Under Section 501(c)(3) of the Internal Revenue Code: http://www.irs.gov/pub/irs-pdf/f1023.pdf
Form 990: Return of Organization Exempt from Income Tax: http://www.irs.gov/pub/irs-pdf/f990.pdf
Annual Electronic Filing Requirement for Small Exempt Organization, Form 990-N (E-Postcard): http://www.irs.gov/charities/article/0,,id=169250,00.html
Form 990-PF: Return of Private Foundation or Section 4947(a)(1) Nonexempt Charitable Trust Treated as a Private Foundation: http://www.irs.gov/pub/irs-pdf/f990pf.pdf
Form 4720: Return of Certain Excise Taxes Under Chapters 41 and 42 of the Internal Revenue Code [applicable to Private Foundations]: http://www.irs.gov/pub/irs-pdf/f4720.pdf
U.S. Department of the Treasury Anti-Terrorist Financing Guidelines:
Voluntary Best Practices for U.S.-Based Charities: http://www.treasury.gov/resource-center/terrorist-illicit-finance/Documents/guidelines_charities.pdf
Exempt Organizations Provisions – Internal Revenue Code (Title 26, United States Code): http://www.irs.gov/pub/irs-tege/eo_code_provisions.pdf
Exempt Organizations Provisions – Federal Tax Regulations (Title 26, Code of Federal Regulations): http://www.irs.gov/pub/irs-tege/eo_regs.pdf
Current Revenue Procedures Pertaining To Exempt Organizations: http://www.irs.gov/pub/irs-tege/eorevenueprocedures.pdf