A W-2 is a form given by an employer to every employee who earned at least $600 in a year, or who had tax withheld. It lists wages paid to the employee, along with taxes withheld, and related information for an entire calendar year. The W-2 form is used to file an Income Tax return, and is normally provided by January 31st for the previous year. A copy is also provided by the employer to the Internal Revenue Service.