The Sixteenth Amendment, passed in 1913, is probably one of the least well-known and yet most unpopular amendments, as it grants Congress the ability to levy a federal income tax. While the first federal income tax was levied during the Civil War as a result of the Revenue Act of 1861 (replaced the following year), the annual income tax has been alive and well for over a century. Oliver Wendell Holmes Jr’s quote in its defense — “Taxes are what we pay for civilized society” — is engraved on the front of the I.R.S. headquarters in Washington, D.C.