Applicable to the United States, an Employer Identification Number or EIN (also known as Federal Employer Identification Number or (FEIN)) is the corporate equivalent to a Social Security Number, although it is issued to anyone, including individuals, who has to pay withholding taxes on employees.

Also known as the Tax Identification Number (TIN), Federal Employer Identification Number (FEIN) or the Federal Tax Identification Number, the EIN is a unique nine-digit number assigned by the Internal Revenue Service (IRS) to business entities operating in the United States for the purposes of identification. When the number is used for identification rather than employment tax reporting, it is usually referred to as a TIN, and when used for the purposes of reporting employment taxes, it is usually referred to as an EIN.^{[citation needed]} This article will use the latter term.

Similar in purpose to the Social Security Number assigned to individuals, EINs are used by employers, sole proprietors, corporations, partnerships, non-profit organizations, trusts and estates, government agencies, certain individuals and other business entities. The IRS uses this number to identify taxpayers that are required to file various business tax returns. Individuals who are employers may choose to either obtain an EIN or use their Social Security Number for the purpose of reporting taxes withheld on behalf of their employees. Contrary to some misconceptions, credit bureaus and credit issuers can tell the difference between SSN and EIN Numbers. SSN Numbers can be validated as to origin and state / year of issuance. The credit bureaus and issuers are highly trained in fraud detection, and increasingly sophisticated algorithms and protections are used. This is why the EIN is not considered sensitive information, and is freely distributed by many businesses by way of publications and the internet.