The Sixteenth Amendment to the United States Constitution is ratified, authorizing the Federal government to impose and collect an income tax.

The Sixteenth Amendment to the United States Constitution allows Congress to levy an income tax without apportioning it among the states on the basis of population. It was passed by Congress in 1909 in response to the 1895 Supreme Court case of Pollock v. Farmers' Loan & Trust Co. The Sixteenth Amendment was ratified by the requisite number of states on February 3, 1913, and effectively overruled the Supreme Court's ruling in Pollock.

The federal government of the United States is the national government of the United States.

An income tax is a tax imposed on individuals or entities (taxpayers) in respect of the income or profits earned by them. Income tax generally is computed as the product of a tax rate times the taxable income. Taxation rates may vary by type or characteristics of the taxpayer and the type of income.