What Is a Federal ID Number?

Federal tax identification numbers, also called employer identification numbers, are issued by the Internal Revenue Service to identify business entities. EINs are required for filing all tax documents, including annual returns, notices and withholding certificates. Certain estates and trusts are also required to obtain EINs for filing purposes.

To obtain an EIN, a responsible party, such as the business entity's principal officer, partner, owner or a nominee, who is given limited authority to act on behalf of the entity, can apply by mail, phone or fax or online. When applying by mail or fax, applicants must complete the Application for Employer Identification Number, form SS-4. Those who apply online receive their EIN immediately upon completion of the application session.