The IMSA organization was founded in 1969 and one race was organized that year. In year 1971 the first IMSA season with six races appeared. GT cars similar to European groups A4 and A2 were starting in the early seasons and were divided into four groups: GTO, GTU, TO and TU. The first champions were Gregg/Haywood in Porsche 914/6 GTU. Usual winners of the early years of IMSA were Porsche 911/Carrera RSR and Chevrolet Corvette.
Later new premier group GTX brings absolute dominance of Porsche 935, which became the most successful car in this series. The most successful driver of seventies was Peter Gregg, champion 1971,'73,'74,'75,'78 and '79.
In 1981 appeared prototypes in new category GTP and Brian Redman was the first champion of IMSA driving prototype Lola T600 Chevrolet. In GTP started also March (champions 1983 - Al Holbert, 1984 - Randy Lanier). In 1984 firstly started new Porsche 962 which became best car between 1985-1987. After that started a Nissan's era with Geoff Brabham at the wheel. Toyota's drivers were quickest at 1992 and 1993 but it was the end of GTP - prototypes. For all this period of GTP-racing Jaguar's tried to be the best. Firstly it was American Group 44 car, later Tom Walkinshaw's TWR-Jaguars. They won many races but never became champions. There were also some other big manufacturers in GTP class such as BMW, Ford, Chevrolet-Lola later Mazda. Along with GTP cars was in 1985 restarted Camel Lights prototype category where Argo's drivers were first champions, later beaten by Spice's drivers. Well known were also Tiga, Royale, Alba, Fabcar and later Kudzu.
IMSA got quite new face in 1994 when new open top WSC sportscars replaced previous GTP and Lights closed cars. The quickest were new Ferrari 333SP prototype but the first WSC champion was Wayne Taylor with Kudzu because Ferrari weren't ready to start in early season races at Daytona and Sebring. In 1995 new rival for Ferrari appeared - Riley & Scott Mk III. And only these two models were able to win any race till demise of IMSA in 1998.
During 1997 season was IMSA renamed to Professional SportsCar Racing (PSCR) and was know under this name till end of 1998. For the 1999 season SPORTS CAR - the sanctioning body - decided to drop their own championship to sanction new American Le Mans Series which arose from initiative of Mr. Don Panoz.
In IMSA always existed many groups with separate classifications. Each era had its top class, firstly GTO, later GTX, GTP and finally WSC. Other categories had sometimes their own separate races, while all categories together started usually only in long distance races such as 24 Hours of Daytona or 12 Hours of Sebring.
Many years were GT cars in IMSA running in two categories. GTO were Grand Touring cars over 2.5 litres and GTU cars Grand Touring under 2.5 litres. In 1992 premier GT category was renamed to GTS because of sponsor and GTO title was used for former American Challenge cars which supported IMSA GT races for many years. New GT categories were established in 1995 to move close to european rules - GTS-1 and GTS-2. In 1997 GTS-2 became GTS-3 and new GTS-2 group was announced. Here are results of GT races that were run separately.
IMSA as sanctioning body organized not only Camel GT Championship but also many others less important championships. One of them was Bridgestone Supercar Championship that was for super GT cars like Porsche 911 Turbo, Nissan 300ZX-T or Lotus Esprit and during its existence some famous drivers took part in: Hans-Joachim Stuck, Hurley Haywood, "John Winter", Ellio Forbes-Robinson and others.