Currently, there are 7 Call of Duty Games belonging to the main series. This would include the Call Of Duty Finest Hour, Call of Duty 2: Big Red One, Call of Duty 3, Call of Duty 4: Modern Warfare, Call of Duty: World at War, Call of Duty: Modern Warfare 2, and Call of Duty: Black Ops. There are plans to release a Call of Duty: Modern Warfare 3 which would form the 8th installment to the series. The numbers would change, however, if you wold include the expansion which is the Call of Duty: United Offensive, to the game as well as those that were meant for consoles and other handheld devices. You can read more about the various installments to this series at http://www.ask.com/wiki/Call_of_Duty.