A surgical instrument, comprising: an elongate shaft assembly defining a shaft axis; a surgical end effector pivotally coupled to said elongate shaft assembly for selective articulation relative to said elongate shaft assembly about an articulation axis that is transverse to said shaft axis; and an articulation system comprising: an articulation cable coupled to said surgical end effector at a point of attachment and journaled on a proximal pulley supported on said elongate shaft assembly, said proximal pulley defining a proximal pulley axis located a tension distance from said point of attachment; an articulation driver coupled to said articulation cable for selectively causing said articulation cable to rotate about said proximal pulley in first and second articulation directions; and an adjustable tensioning assembly interfacing with said proximal pulley to selectively adjust said tension distance, wherein said adjustable tensioning assembly comprises: a pulley mount supporting said proximal pulley thereon; characterised in that said adjustable tensioning assembly further comprises: a mounting shaft coupled to said pulley mount and supported in a portion of said elongate shaft assembly for selective rotation relative thereto, said mounting shaft being eccentrically attached to said pulley mount such that rotation of said mounting shaft causes said proximal pulley to move axially to adjust said tension distance between said proximal pulley axis and said point of attachment. an elongate shaft assembly defining a shaft axis; a surgical end effector pivotally coupled to said elongate shaft assembly for selective articulation relative to said elongate shaft assembly about an articulation axis that is transverse to said shaft axis; and an articulation system comprising: an articulation cable coupled to said surgical end effector at a point of attachment and journaled on a proximal pulley supported on said elongate shaft assembly, said proximal pulley defining a proximal pulley axis located a tension distance from said point of attachment; an articulation driver coupled to said articulation cable for selectively causing said articulation cable to rotate about said proximal pulley in first and second articulation directions; and an adjustable tensioning assembly interfacing with said proximal pulley to selectively adjust said tension distance, wherein said adjustable tensioning assembly comprises: a pulley mount supporting said proximal pulley thereon; characterised in that said adjustable tensioning assembly further comprises: a mounting shaft coupled to said pulley mount and supported in a portion of said elongate shaft assembly for selective rotation relative thereto, said mounting shaft being eccentrically attached to said pulley mount such that rotation of said mounting shaft causes said proximal pulley to move axially to adjust said tension distance between said proximal pulley axis and said point of attachment. an articulation cable coupled to said surgical end effector at a point of attachment and journaled on a proximal pulley supported on said elongate shaft assembly, said proximal pulley defining a proximal pulley axis located a tension distance from said point of attachment; an articulation driver coupled to said articulation cable for selectively causing said articulation cable to rotate about said proximal pulley in first and second articulation directions; and an adjustable tensioning assembly interfacing with said proximal pulley to selectively adjust said tension distance, wherein said adjustable tensioning assembly comprises: a pulley mount supporting said proximal pulley thereon; characterised in that said adjustable tensioning assembly further comprises: a mounting shaft coupled to said pulley mount and supported in a portion of said elongate shaft assembly for selective rotation relative thereto, said mounting shaft being eccentrically attached to said pulley mount such that rotation of said mounting shaft causes said proximal pulley to move axially to adjust said tension distance between said proximal pulley axis and said point of attachment. a pulley mount supporting said proximal pulley thereon; characterised in that said adjustable tensioning assembly further comprises: a mounting shaft coupled to said pulley mount and supported in a portion of said elongate shaft assembly for selective rotation relative thereto, said mounting shaft being eccentrically attached to said pulley mount such that rotation of said mounting shaft causes said proximal pulley to move axially to adjust said tension distance between said proximal pulley axis and said point of attachment.