In the first season of Grand Am competition there were five classes but in 2005 the series had reduced the number to two categories:

• Daytona Prototype (DP): This class was introduced in 2003 and was established to replace the two existing Sports Racing Prototype groups. To control costs, the cars used a tube frame chassis rather than the expensive composites used to construct most prototype race cars. Also, expenses were contained by limiting modifications and implementing rules that would be in place for five years. Approved to produce the first generation of Daytona Prototypes - for a cost of approximately $400,000 were: Riley Technologies, Doran Designs, Crawford Race Cars, Fabcar Engineering, Chase Competition Engineering, Picchio and Multimatic. Costs were also controlled by restricting the engines to production based motors supplied by Pontiac, Lexus, BMW, Porsche, Ford and Infiniti. Engine displacement was used to determine the weight of a car and whether a five or six-speed transmission could be utilized.
• Grand Touring (GT): In 2004, there were two production-based classes: Grand Touring and Super Grand Sport which initially competed in the Grand Am Cup division. These two categories were combined into a single class in 2005. Participating in this group are manufacturers such as Porsche, BMW, Chevrolet, Mazda, Ferrari and Pontiac. As with the Daytona Prototypes, engine displacement was used to establish the weight of different makes and models.

As in the past, the season opened in January with the Rolex 24 at Daytona International Speedway and ended in Utah at Miller Motorsports Park. In between these two venues, there were events at Autodromo Hermanos Rodriguez, Homestead-Miami Speedway, Long Beach, Mazda Raceway Laguna Seca, Lime Rock Park, Watkins Glen, Barber Motorsports Park, Mid-Ohio, Virginia International Raceway, Phoenix International Raceway and Infineon Raceway. There was a total of fifteen events with the series competing at Daytona and Watkins Glen twice.

The event a Watkins Glen International began with controversy. An injunction granted to Krohn Racing and driver Colin Braun by the New York State Supreme Court cancelled Thursday's Daytona Prototype practice sessions. The issue was a contract between the Indy Racing League (IRL) and Watkins Glen International, which prohibited competitors under 18-years old from competing in any on-track activities at the same racing facility and on the same weekend as an IRL event. It was mandated that a minor is not allowed to race at the facility when it is sponsored by a tobacco company. One of the IRL’s high profile teams, Penske Racing, was sponsored by Marlboro cigarettes. Krohn Racing employed 17-year old Colin Braun as a driver.

With the prospect of Grand Am teams not being allowed to race until Monday, team principal, Tracy Krohn decided to drop the case and the event was able to continue with some adjustments to the schedule.