Federal tax law begins (and ends!) with the Internal Revenue Code (IRC or “Tax Code”), which was enacted by Congress in Title 26 of the United States Code (26 U.S.C. et seq). The Tax Code, formally known as the Internal Revenue Code of 1986, contains the federal domestic statutory tax law of the United States.
The Internal Revenue Code is organized by such topics as income tax, payroll tax, estate tax, gift tax, and excise tax. The Tax Code also contains rules for procedure and administration. As everyone soon finds out after earning their first paycheck, if not sooner, the agency responsible for administering its rules and associated regulations is the Internal Revenue Service, aka IRS.