Sixteenth Amendment to the United States Constitution

Amendment XVI (the Sixteenth Amendment) of the United States Constitution, authorizing a graduated income tax, was ratified on February 3, 1913. It states:

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.

Interpretation and history

This amendment establishes the constitutionality of the federal income tax.

There is some academic dispute as to whether proper procedure was followed in the ratification of this amendment.

http://www.archives.gov/exhibit-hall/charters-of-freedom/constitution/amendments-11-27.html#16