A surgical stapler comprising: a handle assembly; an elongated body extending from the handle assembly; an articulable tool assembly mounted on a distal end of the elongated body; and an articulation mechanism operably connected to the handle assembly and configured to selectively articulate and securely lock the tool assembly in one or more positions, the articulation mechanism having: a main shaft member mounted for rotation and connected to an articulation linkage; a rotationally fixed retainer having an opening for receiving a shaft portion of the main shaft member; characterised by a cam lock having a bore configured to receive the shaft portion of the main shaft member, the cam lock having cam locking surfaces and a locking tab; a biasing member disposed between the retainer and cam lock; a locking cover defining recesses for receiving the locking tab, the recesses including a central recess positioned to correspond to an non-articulated position; an articulation handle having cam surfaces configured to engage the cam locking surfaces of the cam lock, wherein the engagement of the cam locking surfaces and the cam surfaces disengages the cam lock against the bias of the biasing member, and wherein the articulation handle is rotatable from an initial position to a second position whereupon at the second position the articulation lever mechanically engages the main shaft, so that further rotation of the articulation handle causes rotation of the main shaft. a handle assembly; an elongated body extending from the handle assembly; an articulable tool assembly mounted on a distal end of the elongated body; and an articulation mechanism operably connected to the handle assembly and configured to selectively articulate and securely lock the tool assembly in one or more positions, the articulation mechanism having: a main shaft member mounted for rotation and connected to an articulation linkage; a rotationally fixed retainer having an opening for receiving a shaft portion of the main shaft member; characterised by a cam lock having a bore configured to receive the shaft portion of the main shaft member, the cam lock having cam locking surfaces and a locking tab; a biasing member disposed between the retainer and cam lock; a locking cover defining recesses for receiving the locking tab, the recesses including a central recess positioned to correspond to an non-articulated position; an articulation handle having cam surfaces configured to engage the cam locking surfaces of the cam lock, wherein the engagement of the cam locking surfaces and the cam surfaces disengages the cam lock against the bias of the biasing member, and wherein the articulation handle is rotatable from an initial position to a second position whereupon at the second position the articulation lever mechanically engages the main shaft, so that further rotation of the articulation handle causes rotation of the main shaft. a main shaft member mounted for rotation and connected to an articulation linkage; a rotationally fixed retainer having an opening for receiving a shaft portion of the main shaft member; characterised by a cam lock having a bore configured to receive the shaft portion of the main shaft member, the cam lock having cam locking surfaces and a locking tab; a biasing member disposed between the retainer and cam lock; a locking cover defining recesses for receiving the locking tab, the recesses including a central recess positioned to correspond to an non-articulated position; an articulation handle having cam surfaces configured to engage the cam locking surfaces of the cam lock, wherein the engagement of the cam locking surfaces and the cam surfaces disengages the cam lock against the bias of the biasing member, and wherein the articulation handle is rotatable from an initial position to a second position whereupon at the second position the articulation lever mechanically engages the main shaft, so that further rotation of the articulation handle causes rotation of the main shaft.