The International Motorsports Association Grand Touring Series, or IMSA GT, was a sports car series that lasted from 1971-1999. It was the premier sports car racing league in the US in its time, providing both production sports cars and IMSA GT Prototypes. In 2000 it split into the Rolex Sports Car Series, which uses the old format of the ISMA GT Series, and the American Le Mans Series, the direct descendant of the league. Both leagues received two endurance races each.