The Sixteenth Amendment to the United States Constitution, ratified on 3 February 1913, reads in full: “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.” It grants Congress the power to levy a federal income tax on individuals and corporations without apportioning it among the states by population and without regard to any census or enumeration. The amendment overturned the Supreme Court's 1895 ruling in Pollock v. Farmers' Loan & Trust Co., which had held that a federal income tax on income derived from property was a direct tax requiring apportionment under Article I.

The federal government had levied income taxes before the amendment's ratification. Congress enacted an income tax during the Civil War under the Revenue Act of 1861, which was later repealed. A subsequent income tax passed in 1894 was struck down in Pollock. The Pollock decision created a constitutional barrier that reformers sought to remove through amendment. President William Howard Taft proposed the amendment to Congress in 1909, and it was sent to the states for ratification. Forty-two of the then-48 states ratified it; six did not. A full account of the political and legal history leading to ratification is at Sixteenth Amendment - History.

The amendment authorizes taxation of income “from whatever source derived,” language courts have interpreted broadly. The Supreme Court has held that Congress may tax wages, salaries, business profits, capital gains, rents, dividends, and most other economic gains. What constitutes “income” as opposed to a return of capital has been the subject of ongoing litigation and scholarly debate. The amendment does not define “income,” leaving that task to Congress and the courts.

A minority legal viewpoint holds that the amendment did not actually expand Congress's taxing power but merely clarified the apportionment requirement, and some tax protesters have advanced arguments - consistently rejected by federal courts - that the amendment was not properly ratified or does not apply to wages. These positions are addressed at Sixteenth Amendment - Ratification Debate.

The amendment provides the constitutional foundation for the modern federal income tax system, which funds the majority of federal government operations. Debates over income tax policy - including rate structures, the progressive versus flat tax question, deductions and credits, corporate taxation, and the treatment of capital gains - are ongoing and do not implicate the amendment's validity but rather Congress's choices within its authority. The broader question of what tax policy the federal government should pursue falls under Tax Policy.

• Necessary correction to Pollock: The amendment restored what many considered the original understanding of federal taxing power and enabled a more equitable distribution of the tax burden. See Sixteenth Amendment - Necessary Correction Viewpoint-viewpoint.
• Expansion of federal power: Critics argue the amendment fundamentally altered the federal-state balance by giving Congress a broad and largely unchecked revenue source, contributing to the growth of the administrative state. See Sixteenth Amendment - Federal Power Expansion Viewpoint-viewpoint.
• Flat tax and reform: Some argue the amendment's broad grant of taxing power has enabled a tax code of excessive complexity and that structural reform - including a flat tax or consumption tax - is warranted. See Tax Reform - Flat Tax Viewpoint-viewpoint.
• Improper ratification: A fringe legal argument holds that the amendment was not validly ratified by the required number of states. Federal courts have consistently rejected this position. See Sixteenth Amendment - Ratification Debate.

• Sixteenth Amendment - History
• Sixteenth Amendment - Ratification Debate
• Tax Policy
• Tax Reform - Debate
• Tax Reform - Flat Tax Viewpoint-viewpoint
• Pollock v. Farmers' Loan & Trust Co.
• United States - History
• Federal Income Tax

1. U.S. Const. amend. XVI.
2. Pollock v. Farmers' Loan & Trust Co., 157 U.S. 429 (1895), aff'd on reh'g, 158 U.S. 601 (1895).
3. Revenue Act of 1861, ch. 45, 12 Stat. 292 (1861).
4. Taft, William Howard. Message to Congress, 16 June 1909. Congressional Record, 61st Cong., 1st Sess.
5. Eisner v. Macomber, 252 U.S. 189 (1920) (discussing the meaning of “income” under the Sixteenth Amendment).
6. United States v. Sullivan, 274 U.S. 259 (1927); Commissioner v. Glenshaw Glass Co., 348 U.S. 426 (1955) (broad interpretation of income).
7. United States v. Collins, 920 F.2d 619 (10th Cir. 1990) (rejecting ratification challenge as frivolous).