A surgical stapling instrument, comprising: a shaft; an end effector extending from said shaft, said end effector comprising: a first jaw comprising a distal jaw end; and a second jaw movable relative to said first jaw between an open position and a closed position; a firing assembly movable toward said distal jaw end during a firing stroke, wherein said firing assembly comprises: a coupling portion configured to engage said first jaw and said second jaw during said firing stroke; a firing bar configured to push said coupling portion; and a lockout bar comprising a distal lockout end, wherein said lockout bar is movable between a distal locked position and a proximal unlocked position; a lock in said shaft, wherein said lock is engaged with said firing bar prior to said firing stroke when said lockout bar is in said distal locked position, and wherein said lock is disengaged from said firing bar prior to said firing stroke when said lockout bar is in said proximal unlocked position; and a staple cartridge positionable in said first jaw, wherein said staple cartridge comprises: a cartridge body; a plurality of staples removably stored in said cartridge body; and a sled movable between a proximal unfired position and a distal fired position to eject said staples from said cartridge body during said firing stroke, wherein said sled is configured to push said lockout bar into said proximal unlocked position when said staple cartridge is loaded into said first jaw and said sled is in said proximal unfired position, thereby disengaging said lock from said firing bar. a shaft; an end effector extending from said shaft, said end effector comprising: a first jaw comprising a distal jaw end; and a second jaw movable relative to said first jaw between an open position and a closed position; a first jaw comprising a distal jaw end; and a second jaw movable relative to said first jaw between an open position and a closed position; a firing assembly movable toward said distal jaw end during a firing stroke, wherein said firing assembly comprises: a coupling portion configured to engage said first jaw and said second jaw during said firing stroke; a firing bar configured to push said coupling portion; and a lockout bar comprising a distal lockout end, wherein said lockout bar is movable between a distal locked position and a proximal unlocked position; a coupling portion configured to engage said first jaw and said second jaw during said firing stroke; a firing bar configured to push said coupling portion; and a lockout bar comprising a distal lockout end, wherein said lockout bar is movable between a distal locked position and a proximal unlocked position; a lock in said shaft, wherein said lock is engaged with said firing bar prior to said firing stroke when said lockout bar is in said distal locked position, and wherein said lock is disengaged from said firing bar prior to said firing stroke when said lockout bar is in said proximal unlocked position; and a staple cartridge positionable in said first jaw, wherein said staple cartridge comprises: a cartridge body; a plurality of staples removably stored in said cartridge body; and a sled movable between a proximal unfired position and a distal fired position to eject said staples from said cartridge body during said firing stroke, wherein said sled is configured to push said lockout bar into said proximal unlocked position when said staple cartridge is loaded into said first jaw and said sled is in said proximal unfired position, thereby disengaging said lock from said firing bar. a cartridge body; a plurality of staples removably stored in said cartridge body; and a sled movable between a proximal unfired position and a distal fired position to eject said staples from said cartridge body during said firing stroke, wherein said sled is configured to push said lockout bar into said proximal unlocked position when said staple cartridge is loaded into said first jaw and said sled is in said proximal unfired position, thereby disengaging said lock from said firing bar.