A surgical instrument insertable through a trocar, wherein said surgical instrument comprises: a handle; and a shaft extending from said handle, comprising: a frame; a proximal portion connected to said handle; a distal portion comprising an end effector; an articulation joint, wherein said end effector is rotatable about said articulation joint; an articulation actuator (10310, 11310) operably coupled to said end effector, wherein said articulation actuator is selectively movable to rotate said end effector in a first direction and a second direction; an outer housing slidable relative to said frame, comprising: a distal non-round housing portion adjacent said articulation joint; and a longitudinal round housing portion extending between said proximal portion and said distal non-round housing portion, wherein said longitudinal round housing portion comprises a first diameter, wherein said distal non-round housing portion comprises a second diameter, wherein said first diameter is less than said second diameter, and wherein said distal non-round housing portion and said longitudinal round housing portion are sized and configured to be inserted through the trocar into a surgical site; and an articulation lock configured to engage said articulation actuator and prevent the rotation of said end effector, wherein said articulation lock is positioned within said distal non-round housing portion. a handle; and a shaft extending from said handle, comprising: a frame; a proximal portion connected to said handle; a distal portion comprising an end effector; an articulation joint, wherein said end effector is rotatable about said articulation joint; an articulation actuator (10310, 11310) operably coupled to said end effector, wherein said articulation actuator is selectively movable to rotate said end effector in a first direction and a second direction; an outer housing slidable relative to said frame, comprising: a distal non-round housing portion adjacent said articulation joint; and a longitudinal round housing portion extending between said proximal portion and said distal non-round housing portion, wherein said longitudinal round housing portion comprises a first diameter, wherein said distal non-round housing portion comprises a second diameter, wherein said first diameter is less than said second diameter, and wherein said distal non-round housing portion and said longitudinal round housing portion are sized and configured to be inserted through the trocar into a surgical site; and an articulation lock configured to engage said articulation actuator and prevent the rotation of said end effector, wherein said articulation lock is positioned within said distal non-round housing portion. a frame; a proximal portion connected to said handle; a distal portion comprising an end effector; an articulation joint, wherein said end effector is rotatable about said articulation joint; an articulation actuator (10310, 11310) operably coupled to said end effector, wherein said articulation actuator is selectively movable to rotate said end effector in a first direction and a second direction; an outer housing slidable relative to said frame, comprising: a distal non-round housing portion adjacent said articulation joint; and a longitudinal round housing portion extending between said proximal portion and said distal non-round housing portion, wherein said longitudinal round housing portion comprises a first diameter, wherein said distal non-round housing portion comprises a second diameter, wherein said first diameter is less than said second diameter, and wherein said distal non-round housing portion and said longitudinal round housing portion are sized and configured to be inserted through the trocar into a surgical site; and a distal non-round housing portion adjacent said articulation joint; and a longitudinal round housing portion extending between said proximal portion and said distal non-round housing portion, wherein said longitudinal round housing portion comprises a first diameter, wherein said distal non-round housing portion comprises a second diameter, wherein said first diameter is less than said second diameter, and wherein said distal non-round housing portion and said longitudinal round housing portion are sized and configured to be inserted through the trocar into a surgical site; and an articulation lock configured to engage said articulation actuator and prevent the rotation of said end effector, wherein said articulation lock is positioned within said distal non-round housing portion.