Form W-9 is the IRS form used by a company to request your taxpayer identification number. You may get a blank Form W-9 to fill out if you or your company are hired to provide services to another company. Most often, Form W-9 is sent to independent contractors, consultants, and other self-employed workers.
Filling out a W-9 is pretty straightforward. Just provide your name and Social Security Number, or the name and Employer Identification Number of your business.
By submitting a W-9, you are certifying that the tax id number you are providing is correct and accurate and that you are not subject to backup withholding.
You can obtain a blank Form W-9 (PDF) to give to independent contractors you hire or to type and print out if you need to give one to your employer.