An apparatus for operating on tissue, the apparatus comprising: (a) a body assembly; (b) a shaft extending distally from the body assembly, wherein the shaft defines a longitudinal axis; (c) an acoustic waveguide (180, 280), wherein the waveguide comprises a flexible portion (166, 266); (d) an articulation section coupled with the shaft, wherein a portion of the articulation section encompasses the flexible portion of the waveguide, wherein the articulation section further comprises: (i) a first member, and (ii) a second member, wherein the second member is longitudinally translatable relative to the first member; (e) an end effector (40, 240) comprising an ultrasonic blade in acoustic communication with the waveguide; and (f) an articulation drive assembly operable to drive articulation of the articulation section to thereby deflect the end effector from the longitudinal axis in a first direction; wherein the articulation section further comprises a distal flex member, a proximal flex member, and a plurality of flex base members (306a-c) positioned proximally relative to the distal flex member and distally relative to the proximal flex member; wherein the distal flex member is operably coupled to distal ends of the first and second members (212, 214); characterized in that the distal flex member includes a proximal end, a distal end and a generally U-shaped body that defines a first space configured for receiving at least a portion of the waveguide; the proximal flex member includes a proximal end, a distal end and a generally U-shaped body that defines a second space configured for receiving at least a portion of the waveguide; and the flex base members (306a-c) define a generally U-shaped body and a third space configured for receiving at least a portion of the waveguide; wherein the first, second and third spaces (310, 343, 368) receive the waveguide such that the distal flex member, the proximal flex member, and the flex base members (306a-c) do not contact the waveguide. (a) a body assembly; (b) a shaft extending distally from the body assembly, wherein the shaft defines a longitudinal axis; (c) an acoustic waveguide (180, 280), wherein the waveguide comprises a flexible portion (166, 266); (d) an articulation section coupled with the shaft, wherein a portion of the articulation section encompasses the flexible portion of the waveguide, wherein the articulation section further comprises: (i) a first member, and (ii) a second member, wherein the second member is longitudinally translatable relative to the first member; (i) a first member, and (ii) a second member, wherein the second member is longitudinally translatable relative to the first member; (e) an end effector (40, 240) comprising an ultrasonic blade in acoustic communication with the waveguide; and (f) an articulation drive assembly operable to drive articulation of the articulation section to thereby deflect the end effector from the longitudinal axis in a first direction; wherein the articulation section further comprises a distal flex member, a proximal flex member, and a plurality of flex base members (306a-c) positioned proximally relative to the distal flex member and distally relative to the proximal flex member; wherein the distal flex member is operably coupled to distal ends of the first and second members (212, 214); characterized in that the distal flex member includes a proximal end, a distal end and a generally U-shaped body that defines a first space configured for receiving at least a portion of the waveguide; the proximal flex member includes a proximal end, a distal end and a generally U-shaped body that defines a second space configured for receiving at least a portion of the waveguide; and the flex base members (306a-c) define a generally U-shaped body and a third space configured for receiving at least a portion of the waveguide; wherein the first, second and third spaces (310, 343, 368) receive the waveguide such that the distal flex member, the proximal flex member, and the flex base members (306a-c) do not contact the waveguide. the articulation section further comprises a distal flex member, a proximal flex member, and a plurality of flex base members (306a-c) positioned proximally relative to the distal flex member and distally relative to the proximal flex member; wherein the distal flex member is operably coupled to distal ends of the first and second members (212, 214); characterized in that the distal flex member includes a proximal end, a distal end and a generally U-shaped body that defines a first space configured for receiving at least a portion of the waveguide; the proximal flex member includes a proximal end, a distal end and a generally U-shaped body that defines a second space configured for receiving at least a portion of the waveguide; and the flex base members (306a-c) define a generally U-shaped body and a third space configured for receiving at least a portion of the waveguide; wherein the first, second and third spaces (310, 343, 368) receive the waveguide such that the distal flex member, the proximal flex member, and the flex base members (306a-c) do not contact the waveguide.