Call of Duty is the world's best-selling video game franchise. When it was first released, it focused on games set in World War II. As the franchise grew, the series has seen games set amid the Cold War, futuristic worlds, and outer space. When two teams compete in a professional match of Call of Duty, they play three separate modes on different maps. Winning a game earns a team one match point. Each match is a best-of-five series.