Form W-9 is a request for your tax ID number. You might want to get an EIN for your self-employment business and put the EIN on the W-9 instead of your Social Security number, just so that you don't have to give the company your Social Security number.
EIN stands for Employer Identification Number, but you do not have to be an employer to get one. You can apply for an EIN online on the IRS web site and get it right away.
