The NASCAR NEXTEL Cup Series is the sport's highest level of professional competition, and consequently it is 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 although ambiguous, the use of "NASCAR" as a synonym for the NEXTEL Cup series is common.

The NASCAR Busch Series is the second highest level of professional competition in NASCAR. This level is considered to be the "minor leagues" of stockcar racing (and coincidentally, the sponsor Busch matches the term "bush league") The cars are very similar to Nextel Cup with only a few differences, such as the weight of the car. 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, several NEXTEL Cup drivers have tried to run races in both series, using the Busch race as a practice. Martin Truex, Jr. won the title in 2005, and Kevin Harvick set the record for the earliest clinching of the title in NBS history in 2006. The Busch series is currently looking for a new title sponsor for the 2008 season and beyond.

The NASCAR Craftsman Truck Series is a popular NASCAR racing series that features modified pickup trucks. It is one of the three national divisions of NASCAR, together with the Busch Series and the Nextel Cup.

The NASCAR Craftsman Truck Series was formed in 1994. In 1994 NASCAR announced the formation of the NASCAR SuperTruck Series presented by Craftsman ,with the first series race in 1995. In 1996 it was renamed the NASCAR Craftsman Truck Series because of Craftsman's involvement.

The series distinguishes itself from the two other top series in NASCAR by using a heavily modified version of a pickup truck instead of a car. The series was first considered something of an oddity or a "senior's tour" for NASCAR drivers, but eventually grew in popularity and has produced Nextel Cup series drivers who had never raced in the Busch Series.