Form W-9—Request for Taxpayer Identification Number and Certification—is one of the most commonly used IRS forms. If you’ve ever been an employee of a company, you’ve probably completed a Form W-9. True to its name, individuals and entities use the form to provide their taxpayer identification number to entities that will pay them income during the tax year. Your employer uses your W-9 for payroll purposes but doesn't send the form to the Internal Revenue Service. The information is used to prepare employee paychecks during the year and W-2 forms at the end of the year. If you have your own business or work as an independent contractor, a client may request that you provide a W-9 so they can accurately report the payments they make to you.