An ITIN is a tax processing number issued by the Internal Revenue Service (IRS) in the United States to individuals who are required to have a U.S. taxpayer identification number but are not eligible for a Social Security Number (SSN). ITINs are often used by non-resident aliens, resident aliens, and their dependents for tax reporting purposes, such as filing tax returns or claiming certain tax benefits. They help individuals fulfill their tax obligations even if they don’t have an SSN.