If you’re starting a business and will have employees, you need an EIN (Employer Identification Number). It’s also known as a Federal Tax Identification Number.
If you have been a sole proprietorship with only your social security number for identity, in this age of identity fraud, you should consider getting an EIN. The government has made it simple.
You can determine your need for an EIN online. This page has useful information and links: http://www.irs.gov/businesses/small/article/0,,id=102767,00.html
The number is assigned by the IRS and will be used on ALL tax filings.