A stapling unit for use with an endoscopic stapling system adapted to be advanced along an endoscope to a predetermined location within a body lumen to staple the portion of tissue, as part of an occlusal or full thickness resectioning procedure. The stapling unit comprises a first casing having a distal end, a proximal end and a stapling device mounted thereto adjacent to a first window extending through a periphery of the first casing. The invention includes methods for the stapling, severing and removal of tissue by using the device.