The Auto Club 500 is a NASCAR Nextel Cup stock car race held at the California Speedway in Fontana, California. This is one of two races held at the California Speedway, the other being the Sony HD 500. Prior to 2005, the race was held in May. When the NASCAR Realignment of that year was made, the race was moved to February.

The California Speedway is a two-mile, low-banked, D-shaped oval superspeedway in Fontana, California, similar to that of "sister track" Michigan International Speedway. It is located approximately 40 miles east of Los Angeles on the site of the former Kaiser Steel mill. It is a relatively new race track, opening in early 1997, and has additional configurations and facilities to accommodate "road" races, motorcycle races, vehicle testing, and drag races (Auto Club Dragway). This racetrack is a stones throw from the old Ontario Motor Speedway and the old Riverside International Raceway. After Riverside's closure in 1988, Southern California did not host a NASCAR race from 1988 to 1997. Then California Speedway was opened, and racing was back in SoCal.

In addition to NASCAR, the raceway has also hosted open-wheel events from both CART and the Indy Racing League. In 1999 Canadian driver Greg Moore was killed in a crash at the track, resulting in a major overhaul of the backstretch for safety (it was discovered Moore's car slid in the grass off Turn 2, allowing the car to overturn, and cause the fatal crash; following that, ISC, which had purchased the track, paved that section of backstretch apron in time for the 2000 NASCAR event to prevent cars from sliding in that section, and to allow for drivers to have control of the cars in an incident); in 2003 the Indy Racing League set the highest average speed for any circuit event in motorsports at the track.

Like many modern oval tracks, Fontana also features an infield road-course, which has been used by the Grand American Road Racing Association and by the Japanese Grand Touring Car Championship, with the JGTC race being unique in the fact it was a night race. The GARRA Rolex Sports Car Series no longer goes to this track.

In 2003, RJR dropped its sponsorship of the top series, and NASCAR obtained a sponsorship from NEXTEL, a telecommunications company. The contract was not renewed for several reasons; one, because of the steady decline of revenue of RJR, and two, because cigarette and other forms of tobacco advertising were deemed illegal by the U.S. Congress in 2002. In 2003, the Cup series became known as the NEXTEL Cup.