The Sixteenth Amendment gave Congress clear power to tax individual incomes without apportioning the tax among states.
Ratified in 1913, it states that Congress may tax incomes from whatever source without apportionment among the states or regard to any census. Apportionment had made a nationwide income tax difficult because each state’s share had to match its population.
The amendment followed the Supreme Court’s 1895 decision in Pollock v. Farmers’ Loan & Trust Co., which struck down an earlier federal income-tax law as an unapportioned direct tax. The amendment did not itself establish tax rates or create the Internal Revenue Service; Congress used its new authority through later legislation.
A common mix-up is saying the amendment invented income taxation. Governments had taxed income before 1913, and the United States briefly imposed a federal income tax during the Civil War. The amendment mainly removed a constitutional obstacle to an unapportioned federal income tax.