ATIN means the Adoption Tax Identification Number. It is a temporary number issued by the Internal Revenue Service for the child in a domestic adoption where the adopting taxpayers do not have and/or are unable to obtain the child's Social Security Number (SSN).
An adoption has to be finalized before a person can apply for a social security number for his/her child. An ATIN is a temporary nine-digit number that can be obtained through the Internal Revenue Service using Form W-7A. When the adoption is finalized, a certified copy of the Order of Adoption can be used to obtain a social security card, passport, etc. in place of a birth certificate. The ATIN must not be used after obtaining the child’s SSN.