A surgical instrument comprising: a handle assembly, an elongated shaft assembly mounted to said handle assembly and protruding therefrom, said elongated shaft assembly comprising: an elongated spine member having a distal end configured to be removably coupled to an end effector; a firing tube axially movable on said elongated spine member and interfacing with a firing system supported by said handle assembly to cause said firing tube to selectively move on said spine member such that said firing tube is selectively axially movable from an un-actuated position wherein the distal end of the spine member is removably couplable to a portion of the end effector to a coupled position wherein a distal portion of said firing tube is configured to retain said portion of said end effector in coupled engagement with said distal end of said spine member, and a cutting member movably supported within said elongated shaft assembly and interfacing with a cutting member advancement system supported by said handle assembly for selectively moving said cutting member from a starting position wherein a tissue-cutting edge formed on a distal end thereof is located within a distal end of said firing tube to cutting positions wherein said tissue-cutting edge is distal to said distal end of said firing tube, characterized in that said firing tube is further selectively axially movable to actuated positions to selectively apply at least one actuation motion to an end effector coupled to said distal end of said spine member. a handle assembly, an elongated shaft assembly mounted to said handle assembly and protruding therefrom, said elongated shaft assembly comprising: an elongated spine member having a distal end configured to be removably coupled to an end effector; a firing tube axially movable on said elongated spine member and interfacing with a firing system supported by said handle assembly to cause said firing tube to selectively move on said spine member such that said firing tube is selectively axially movable from an un-actuated position wherein the distal end of the spine member is removably couplable to a portion of the end effector to a coupled position wherein a distal portion of said firing tube is configured to retain said portion of said end effector in coupled engagement with said distal end of said spine member, and a cutting member movably supported within said elongated shaft assembly and interfacing with a cutting member advancement system supported by said handle assembly for selectively moving said cutting member from a starting position wherein a tissue-cutting edge formed on a distal end thereof is located within a distal end of said firing tube to cutting positions wherein said tissue-cutting edge is distal to said distal end of said firing tube, characterized in that said firing tube is further selectively axially movable to actuated positions to selectively apply at least one actuation motion to an end effector coupled to said distal end of said spine member. an elongated spine member having a distal end configured to be removably coupled to an end effector; a firing tube axially movable on said elongated spine member and interfacing with a firing system supported by said handle assembly to cause said firing tube to selectively move on said spine member such that said firing tube is selectively axially movable from an un-actuated position wherein the distal end of the spine member is removably couplable to a portion of the end effector to a coupled position wherein a distal portion of said firing tube is configured to retain said portion of said end effector in coupled engagement with said distal end of said spine member, and a cutting member movably supported within said elongated shaft assembly and interfacing with a cutting member advancement system supported by said handle assembly for selectively moving said cutting member from a starting position wherein a tissue-cutting edge formed on a distal end thereof is located within a distal end of said firing tube to cutting positions wherein said tissue-cutting edge is distal to said distal end of said firing tube, characterized in that said firing tube is further selectively axially movable to actuated positions to selectively apply at least one actuation motion to an end effector coupled to said distal end of said spine member.