A surgical stapling instrument is disclosed. In at least one form, the instrument comprises an end effector, an elongate shaft, and an articulation joint configured to facilitate selective articulation of the end effector in directions transverse to a longitudinal axis. The instrument further comprises a longitudinally-reciprocating firing assembly comprising a firing bar and a knife. The instrument further comprises a firing assembly lockout arrangement on one of a first jaw and a second jaw and is configured to prevent distal advancement of the knife from a starting to an ending position unless an unfired surgical staple cartridge is operably supported in the one of the first and second jaws. The instrument further comprises means for applying a firing motion to the longitudinally-reciprocating firing assembly to drive the knife from the starting to the ending position and return the knife from the ending position to the starting position.