Surgical stapling instruments having surgical stapling cartridges are disclosed. At least one embodiment includes an end effector that has an elongate channel that is configured to operably support a surgical staple cartridge therein and an anvil that is movably supported on the elongate channel between an open position and closed positions in response to an application of opening and closing motions applied thereto. An anvil lock member cooperates with the anvil to retain the anvil in an open position when a staple cartridge has not been installed in the elongate channel and prevent the anvil from moving to a closed position until the staple cartridge has been seated within the elongate channel. Surgical staple cartridges are configured to move the anvil from an open position to an actuatable position when the cartridge has been installed in the end effector.