A federal tax identification number is a nine-digit number assigned specifically to you that identifies your business to the government.

The government requires you to identify your business with either a Social Security Number or the tax ID number on all government forms and official documents.

International companies will not require you to have an EIN, provided their business does not include any U.S.-based employees. Simply shipping products to the United States does not require the number; however, every country has individual tax laws, so be sure to find out about your own. Because there is no penalty for using the tax number, yet there are many provisions requiring it, it's safest to just apply and get it out of the way early. And besides, getting your tax ID number is free.