The NFL distributes approximately 500 pairs of superbowl tickets to fans through an annual Super Bowl random drawing. This is the NFL's only method of distributing superbowl tickets to the general public. Requests for the random drawing are accepted between Feb. 1 and June 1 of each year preceding the game. Requests must be sent via certified or registered mail to:
NFL Super Bowl Tickets 280 Park Ave. New York, NY 10017

Applicants must put their names and addresses on their requests and send only one per household. Duplicate requests are disregarded. Acknowledgement cards are sent out over the summer, and the drawing is held in October. Everyone who entered is notified at that time of the results. Winners receive an invoice for two superbowl tickets - losers receive postcards.

This information courtesy of fantix.com.