Federal income tax was introduced with the Revenue Act of 1861 to help fund the Civil War, and subsequently repealed, re-adopted, and held unconstitutional. In 1913 the Sixteenth Amendment to the United States Constitution was ratified and gave the United States Congress the legal authority to tax all incomes.

The Internal Revenue Service (IRS) is the revenue service of the United States federal government. The IRS oversees the execution of the Internal Revenue Code. The IRS administers the Tax Code by collecting income taxes and advocating taxpayer compliance.

It is a bureau of the Department of the Treasury, and is under the immediate direction of the Commissioner of Internal Revenue. The IRS is responsible for administration of the Internal Revenue Code.

In fiscal year 2012, the IRS collected more than $2.5 trillion in revenue and processed more than 237 million tax returns.