This year's list measures revenue growth from 2004 through 2007. To qualify, companies must have been founded and generating revenue by the first week of 2004, and therefore able to show four full calendar years of sales. Additionally, they had to be U.S.-based, privately held, and independent -- not subsidiaries or divisions of other companies -- as of December 31, 2007. (Since then, a number of companies on the list have gone public or been acquired.) The minimum revenue required for 2004 is $200,000; the minimum for 2007 is $2 million. Revenue figures given in the company profiles correspond to calendar year 2007. Full-time and part-time employees are included in the employee counts; independent contractors are not. As always, Inc. reserves the right to reject applicants for subjective reasons. The companies of the Inc. 500 represent the top tier of the Inc. 5000, which can be found on Inc.com. All applicants for the Inc. 5000 join IncBizNet, Inc.com's online community for private companies.