US Constitution, Article I, section 8, clause 1
The Congress shall have power to lay and collect taxes, duties, imposts and excises, to pay the debts and provide for the common defense and general welfare of the United States.
Amendment XVI
(Ratified February 3, 1913)
The Congress shall have power to lay and collect taxes on incomes, from whatever source derived, without apportionment among the several States, and without regard to any census or enumeration.
Current income taxes are imposed under these constitutional provisions and various sections of Subtitle A of the Internal Revenue Code of 1986, as amended, including 26 U.S.C. § 1 (imposing income tax on the taxable income of individuals, estates and trusts) and 26 U.S.C. § 11 (imposing income tax on the taxable income of corporations).