From Wikipedia, the free encyclopedia - View original article
An Individual Taxpayer Identification Number (or ITIN) is a United States tax processing number issued by the Internal Revenue Service. It is a nine-digit number that begins with the number 9 and has a range of 70 to 99 (excluding 89 and 93) in the fourth and fifth digit, example 9XX-70-XXXX or 9XX-99-XXXX. The IRS issues ITINs to individuals who are required to have a taxpayer identification number but who do not have, and are not eligible to obtain, a Social Security Number.
ITINs are issued regardless of immigration status because both resident and nonresident aliens may have Federal tax return and payment responsibilities under the Internal Revenue Code. Individuals must have a filing requirement and file a valid federal income tax return to receive an ITIN, unless they meet an exception. An ITIN application cannot be filed electronically (efile). The application, in most cases, should be attached to a valid federal income tax return.
An individual who meets eligibility requirements can file an ITIN application himself or herself. This involves submitting IRS form W-7, which records biographical information, along with specific types of valid supporting ID and a tax return. The applicant can apply directly or file with a certifying acceptance agent, who can assist with the application process for a fee. ITINs can also be issued for a spouse or dependents, if documentation and signature requirements are met and they are claimed on a valid tax return.  Effective June 22, 2012 the IRS began requiring most applicants, even those using acceptance agents, to submit original supporting documents or copies certified by their issuing agency. 
The program was created in 1996 for the purpose of tax filing of individuals without a social security account number. Receiving an ITIN number does not in itself confer the right to work and receive income in the United States.
In 2006 1.4 million people used ITIN when filing taxes. Federal tax law prohibits the IRS from sharing data with other government agencies including the Department of Homeland Security, assuring unauthorized aliens that the tax information will be confidential and will not be used to initiate removal procedures.
ITINs are also used by real estate brokers to facilitate mortgages for unauthorized aliens. In addition to use by unauthorized aliens, ITINs are used by foreign investors in United States real estate. Such investors need ITINs to file federal and state tax returns to report rental income. Starting from Jan 2013 IRS now requires original or certified copies of the original documents along with your w7-ITIN application. IRS will not accept NOTORIZED copies of the passport for ITIN application.