The 2015 IndyCar Series season was the 20th season of the IndyCar Series and the 104th season of American open wheel racing. Its premier event was the 99th Indianapolis 500, which was held on May 24. Will Power returned as the reigning champion, while Ryan Hunter-Reay was the defending Indy 500 champion. Chevrolet entered the season as the reigning Manufacturers' champion. Indianapolis 500 and the season finale counted for double points.