An ITIN consists of nine digits, beginning with the number nine (i.e., 9XX-XX-X). Since 1996, the IRS has issued ITINs to taxpayers and their dependents who are not eligible to obtain a Social Security number (SSN).

1862 - President Lincoln signed into law a revenue-raising measure to help pay for Civil War expenses. The measure created a Commissioner of Internal Revenue and the nation's first income tax.

Before 1913, federal government revenues came mainly from taxes on goods—tariffs on imported products and excise taxes on items like whiskey. The burden of these taxes fell heavily on working Americans, who spent a much higher percentage of their income on goods than rich people did.

On July 1, 1862, President Lincoln signed the second revenue measure of the Civil War into law. This law levied internal taxes and established a permanent internal tax system. Congress established the Office of the Commissioner of Internal Revenue under the Department of the Treasury.

This critical system helps IRS assess taxes, generate refunds, update accounts, and more. It was built in the late 1960s, around the same time NASA's Apollo missions were first sending astronauts to the moon.

Publication 17 covers the general rules for filing a federal income tax return. It supplements the information contained in your tax form instruction booklet. It explains the tax law to make sure you pay only the tax you owe and no more.

The origin of the income tax on individuals is generally cited as the passage of the 16th Amendment, passed by Congress on July 2, 1909, and ratified February 3, 1913.