An Individual Taxpayer Identification Number (ITIN) is a tax processing number issued by the Internal Revenue Service (IRS) that allows you to file taxes and claim tax credits. Individuals who are required to have a U.S. taxpayer identification number and are not eligible to obtain a Social Security Number (SSN) are eligible for an ITIN. Low-income Californians who file tax returns with an ITIN are eligible to claim the California Earned Income Tax Credit (CalEITC) and Young Child Tax Credit (YCTC).