NASCAR-sanctioned series

The "NASCAR NEXTEL Cup Series" is the sport's highest level of professional competition. It is consequently the most popular and most profitable NASCAR series. The 2006 NEXTEL Cup season consisted of 36 races over 10 months, with over $4 million in total prize money at stake at each race. Writers and fans often use "Cup" to refer to the NEXTEL Cup series and the ambiguous use of "NASCAR" as a synonym for the NEXTEL Cup series is common. As of 2007, the defending champion is Jimmie Johnson.

In 2004, NEXTEL took over sponsorship of the premier series from R. J. Reynolds, formally renaming it from the Winston Cup to the NEXTEL Cup Series. A new championship points system, "The Chase for the NEXTEL Cup" was also developed, which reset the point standings with ten races to go, making only drivers in the top ten or within 400 points of the leader eligible to win the championship. In 2007, NASCAR announced it was expanding "The Chase" from ten to twelve drivers, eliminating the 400-point cutoff, and giving a ten-point bonus to the top twelve drivers for each of the races they have won out of the first 26. Wins throughout the season will also be worth five more points than in previous seasons. In 2008, the premier series title name will become the Sprint Cup Series, as part of the merger between NEXTEL and Sprint.

The "NASCAR Busch Series" is the second-highest level of professional competition in NASCAR. The cars look very similar to Nextel Cup cars with only a few differences, such as the weight and length of the car, the size of the rear spoiler, and the power output of the engine. For 2007, the champion is "Buschwacker" Carl Edwards, who won the series with two races left on the schedule.

The Busch Series is currently the only series of the top three to race outside the United States and the only series to have ever held points-paying international events. The season is a few races shorter and the prize money is significantly lower. Over the last several years, a number of NEXTEL Cup drivers have tried to run races in both series, using the Busch race as a warm-up to the Cup event at the same facility. Detractors of this practice have labeled such drivers as "Buschwhackers." The Busch sponsorship is set to expire at the end of 2007, and the series will now be sponsored by Nationwide Insurance. Nationwide will also become NASCAR's official insurance agency replacing Allstate.

Craftsman Truck Series

The '"NASCAR Craftsman Truck Series" features modified pickup trucks. It is one of the three national divisions of NASCAR, together with the Busch Series and the Nextel Cup. As of 2007, the defending champion is Todd Bodine. Ron Hornaday is the 2007 champion by a 54 point margin over Mike Skinner. Hornaday has now earned three Craftsman Truck champioships. Hornaday also has the most victories with 33.

In 1994, NASCAR announced the formation of the NASCAR SuperTruck Series presented by Craftsman. The first series race followed in 1995. In 1996, the series was renamed the NASCAR Craftsman Truck Series to emphasize Craftsman's involvement. The series was first considered something of an oddity or a "senior tour" for NASCAR drivers, but eventually grew in popularity and has produced Nextel Cup series drivers who had never raced in the Busch Series.

NASCAR Canadian Tire Series

NASCAR announced the purchase of Canadian racing series CASCAR in September of 2006. The CASCAR Western Series will become NASCAR's fourth-tier series starting in the Fall of 2007.

NASCAR Corona Series

In December of 2006, NASCAR also announced the creation of a new series in Mexico, the NASCAR Corona Series, replacing the existing Desafio Corona Series, to begin in 2007.

Regional racing series

In addition to the five main series, NASCAR operates several other racing circuits.

Many local race tracks across the United States and Canada run under the Whelen All-American Series banner, where local drivers are compared against each other in a formula where the best local track champion of the nation wins the Whelen All-American Weekly Series National Championship. The Whelen All-American series is split into four divisions. Each division champion receives a point-fund money payout and even more goes to the National champion (driver with most points out of the four division winners). The Whelen All-American Series is the base for stock car racing, developing NASCAR names such as Clint Bowyer, Jimmy Spencer, Tony Stewart, the Bodine brothers and many others along the way.

NASCAR also sanctions three regional racing divisions: The Whelen Modified Tour, which races open-wheel "modified" cars in Northern and Southern divisions; the Grand National Division, which races in the Busch East Series (formerly Busch North); and the NASCAR West Series. Grand National cars are similar to Busch Series cars, although they are less powerful. The AutoZone Elite Division, which races late-model cars which are lighter and less powerful than NEXTEL Cup cars, was originally split into four divisions: Northwest, Southwest, Southeast, and Midwest. At the end of 2005, NASCAR announced that the AutoZone Elite Division would be discontinued after the 2006 season due to having trouble securing NASCAR-sanctioned tracks to successfully host AutoZone Elite Division events, plus escalating costs of competing and downsizing of the Division in recent years.

In 2003, NASCAR standardized rules for its AutoZone Elite and Grand National divisions regional touring series as to permit cars in one series to race against cars in another series in the same division. The top 15 (Grand National) or 10 (AutoZone Elite) in each series will race in a one-race playoff, called the NASCAR Toyota All-Star Showdown, to determine the annual AutoZone Elite and Grand National champions. This event has been hosted at Irwindale Speedway in California since its inception.

Many drivers move up through the series before reaching the NEXTEL Cup series. In 2002, over 9,000 drivers had licenses from NASCAR to race at all levels.

The winners of the Dodge Weekly Series National Championship, the four AutoZone Elite Divisions, the two Whelen Modified and Grand National Divisions, and the three national series are invited to New York City in December to participate in Champions Week ceremonies which conclude with the annual awards banquet at the Waldorf-Astoria Hotel.