A surgical instrument comprising: a shell assembly including: a shell housing; a plurality of staples; a staple pusher configured to eject the plurality of staples from the shell housing; a staple actuator configured to engage the staple pusher; a knife member; and a knife carrier supporting the knife member; and an adapter assembly (14, 20) including: a cam ring movable between an engaged position in which the knife carrier engages the cam ring and a disengaged position in which the knife carrier is disengaged from the cam ring; characterised in that the adapter assembly (14, 20) further comprises: a staple band configured to couple to an actuation mechanism for axial displacement, the staple band configured to releasably engage the staple actuator; and a knife band at least partially received within the staple band, the knife band configured to couple with an actuation mechanism for axial displacement; and in that the cam ring is rotatably supported about the knife band, the cam ring being rotatable between the engaged position in which the knife carrier engages the cam ring for concomitant axial displacement with the knife band and the disengaged position. a shell assembly including: a shell housing; a plurality of staples; a staple pusher configured to eject the plurality of staples from the shell housing; a staple actuator configured to engage the staple pusher; a knife member; and a knife carrier supporting the knife member; and a shell housing; a plurality of staples; a staple pusher configured to eject the plurality of staples from the shell housing; a staple actuator configured to engage the staple pusher; a knife member; and a knife carrier supporting the knife member; and an adapter assembly (14, 20) including: a cam ring movable between an engaged position in which the knife carrier engages the cam ring and a disengaged position in which the knife carrier is disengaged from the cam ring; characterised in that the adapter assembly (14, 20) further comprises: a staple band configured to couple to an actuation mechanism for axial displacement, the staple band configured to releasably engage the staple actuator; and a knife band at least partially received within the staple band, the knife band configured to couple with an actuation mechanism for axial displacement; and in that the cam ring is rotatably supported about the knife band, the cam ring being rotatable between the engaged position in which the knife carrier engages the cam ring for concomitant axial displacement with the knife band and the disengaged position. a cam ring movable between an engaged position in which the knife carrier engages the cam ring and a disengaged position in which the knife carrier is disengaged from the cam ring; characterised in that the adapter assembly (14, 20) further comprises: a staple band configured to couple to an actuation mechanism for axial displacement, the staple band configured to releasably engage the staple actuator; and a knife band at least partially received within the staple band, the knife band configured to couple with an actuation mechanism for axial displacement; and in that the cam ring is rotatably supported about the knife band, the cam ring being rotatable between the engaged position in which the knife carrier engages the cam ring for concomitant axial displacement with the knife band and the disengaged position. a staple band configured to couple to an actuation mechanism for axial displacement, the staple band configured to releasably engage the staple actuator; and a knife band at least partially received within the staple band, the knife band configured to couple with an actuation mechanism for axial displacement; and in that the cam ring is rotatably supported about the knife band, the cam ring being rotatable between the engaged position in which the knife carrier engages the cam ring for concomitant axial displacement with the knife band and the disengaged position.