Individual Taxpayer Identification Numbers (ITINs) are nine-digit numbers issued by the IRS so certain taxpayers who do not have a social security number can file a tax return. According to the IRS, approximately 11 million people have received an ITIN. Now, some of these numbers may need to be renewed. ITINs that have not been used on a federal income tax return for three consecutive years will expire on December 31 of the third consecutive year. Under current rules, ITINs not used on a tax return during 2013, 2014, or 2015, will expire on December 31, 2016. In addition, ITINs issued before 2008 will expire on December 31, 2016, even if they have been used on a tax return.