Sanctioning body of sports car prototype racing in the United States. Current categories include World Sports Cars (WSC) a series for purpose-built race cars, GTS-1 for vehicles resembling street cars but which have custom-made chassis and highly modified engines and GTS-2 which are race cars made from street cars but with modified engines, transmissions and suspensions. Major events sanctioned by IMSA include the Rolex 24 Hours of Daytona and 12 Hours of Sebring, the longest running sports car race in the United States.