An employer identification number (EIN) is a number assigned by the IRS to any employer or potential employer. People have social security numbers; businesses have EIN's. If you choose a partnership, S-corporation or limited liability company, you will need an EIN. If you have a sole proprietorship getting an EIN is recommended but optional, unless you have employees in which case an EIN is required. It is recommended that the business is first established legally and fully registered before an application for an EIN is made. For any business type other than a sole proprietorship, an EIN will be required in order to open a bank account.The IRS has made the process quite easy, allowing businesses to apply for an EIN online and get the number quickly. This is a free service provided by the IRS. There are several ways to apply for an EIN: Online: You can apply for the EIN online. The EIN application is processed and an EIN is issued immediately. You should have Adobe Reader installed so you can view, print and/or save the letter assigning your EIN. By MAIL or FAX: – Complete the online Form SS-4, save the completed form, print it out and sign it. Get the address or fax number and mail or fax the completed form. By Telephone (International Applicants): International applicants may call 267-941-1099 from 6:00AM to 11:00PM EST Monday through Friday.