A surgical tool, comprising: a shaft; an end effector; an articulation joint, wherein said end effector is movable relative to said shaft about said articulation joint; and a firing drive, comprising: a rotatable input drive system comprising a threaded transmission portion, wherein said input drive system is rotatable in a first direction and a second direction; and a flexible output shaft comprising: a body comprising a plurality of intrinsic articulation joints; and a thread operably engaged with said threaded transmission portion, wherein said flexible output shaft comprises a longitudinal axis and is constrained from completing a revolution about said longitudinal axis, wherein said rotatable input drive system is configured to translate said flexible output shaft toward said end effector when said rotatable input drive system is rotated in said first direction, and wherein said rotatable input drive system is configured to translate said flexible output shaft away from said end effector when said rotatable input drive system is rotated in said second direction. a shaft; an end effector; an articulation joint, wherein said end effector is movable relative to said shaft about said articulation joint; and a firing drive, comprising: a rotatable input drive system comprising a threaded transmission portion, wherein said input drive system is rotatable in a first direction and a second direction; and a flexible output shaft comprising: a body comprising a plurality of intrinsic articulation joints; and a thread operably engaged with said threaded transmission portion, wherein said flexible output shaft comprises a longitudinal axis and is constrained from completing a revolution about said longitudinal axis, wherein said rotatable input drive system is configured to translate said flexible output shaft toward said end effector when said rotatable input drive system is rotated in said first direction, and wherein said rotatable input drive system is configured to translate said flexible output shaft away from said end effector when said rotatable input drive system is rotated in said second direction. a rotatable input drive system comprising a threaded transmission portion, wherein said input drive system is rotatable in a first direction and a second direction; and a flexible output shaft comprising: a body comprising a plurality of intrinsic articulation joints; and a thread operably engaged with said threaded transmission portion, wherein said flexible output shaft comprises a longitudinal axis and is constrained from completing a revolution about said longitudinal axis, wherein said rotatable input drive system is configured to translate said flexible output shaft toward said end effector when said rotatable input drive system is rotated in said first direction, and wherein said rotatable input drive system is configured to translate said flexible output shaft away from said end effector when said rotatable input drive system is rotated in said second direction. a body comprising a plurality of intrinsic articulation joints; and a thread operably engaged with said threaded transmission portion, wherein said flexible output shaft comprises a longitudinal axis and is constrained from completing a revolution about said longitudinal axis, wherein said rotatable input drive system is configured to translate said flexible output shaft toward said end effector when said rotatable input drive system is rotated in said first direction, and wherein said rotatable input drive system is configured to translate said flexible output shaft away from said end effector when said rotatable input drive system is rotated in said second direction.