IMSA GT was a sports car racing series organized by International Motor Sports Association. Races took place primarily in the United States, and occasionally in Canada. History The series was founded in 1969 by John and Peggy Bishop, and Bill France, Sr. Racing began in 1971, and was originally aimed at two of FIA's stock car categories, running two classes each; the GT (Groups 3 and 4) and touring (Group 1 and 2) classes. The first race was held at Virginia International Raceway; it was an unexpected success, with both the drivers and the handful of spectators who attended. For the following year, John Bishop brought in sponsor R. J. Reynolds, and in 1975 introduced a new category: All American Grand Touring (AAGT). In 1977, the series went through a series of major changes. IMSA permitted turbocharged cars to compete for the first time, as well as introducing a new category: GTX, based on Group 5 rules. In 1981, after Bishop decided to not follow FIA's newly introduced Group C rules, he introduced the GTP class for sports prototypes. In 1989, Bishop sold off his organization. After a period of decline in the early 1990s, the Sports Racer Prototype category was introduced in 1993 to replace the top IMSA GTP category in 1994. In deference to the series deviating from the FIA's naming of the class to Sports Racers and Le Mans Prototypes by the French Automobile Club de l'Ouest (ACO) in Europe for their then separate series, the new class was designated IMSA World Sports Car. After a period of multiple ownerships, the organization, by then owned by Don Panoz, was eventually renamed Professional Sports Car Racing (PSCR). In 1999, PSCR decided to affiliate with the Automobile Club de l'Ouest and adopt the sanctioning body's rule book, renaming the series the American Le Mans Series. Despite having various official names, the GT series was known commonly as the "IMSA series", as it was the sanctioning body. For legal reasons, both the 1999-2013 ALMS and the current WeatherTech SportsCar Championship are regarded as a continuation of the original IMSA GT Championship. Initial divisions The 1971 season was the first racing season, and lasted six races. The early years of the series featured GT cars, similar to the European Group 2 and Group 4 classes, divided into four groups: GTO - Grand touring-type cars with engines of 2.5L displacement or more,