The tax declaration is an obligation of every person who receives income, under certain conditions. In the United States, the individual taxpayer identification number for foreigners (ITIN) allows foreigners to pay taxes, keep their tax situation up to date, and could later be used for other procedures related to staying in this country.
The ITIN was originally designed for tax purposes only. Increasingly, agencies other than the IRS are accepting the ITIN as an identification number. Some private businesses are also accepting ITINs or other documents as proof of identity.