A surgical stapling assembly is disclosed. The surgical stapling assembly comprises a stapling instrument configured to receive a staple cartridge therein. The stapling instrument comprises a first jaw, a second jaw movable relative to the first jaw, a firing member configured to push a sled to deploy staples, and a lockout configured to prevent the firing member from advancing distally when the staple cartridge is not properly seated within the stapling instrument and when the sled of the staple cartridge is not in an unfired position, wherein a lockout key of the staple cartridge defeats a first stage of the lockout when the staple cartridge is fully seated in the stapling instrument, and wherein the sled defeats a second stage of the lockout when the sled is in the unfired position and the staple cartridge is fully seated in the stapling instrument.