An employer identification number (EIN), also known as a tax identification number (TIN), is a nine-digit number assigned to a business entity operating in the United States for identification purposes. Like a Social Security Number for an individual, an EIN is a unique identifier. An EIN is obtained from the IRS and its main purpose is to facilitate the payment of taxes and filing of tax returns by the business entity. However, an EIN is also required for other purposes. For example, financial institutions will not permit a business entity to open a checking or savings account without an EIN.