Abstract: A method and apparatus for manufacturing a square bottom bag is disclosed herein. The method comprises the steps of driving a web in a first direction and bending the web upon itself across its width as it is driven in the first direction to assume a U-shaped configuration, supporting the main panels of the web in the open U-shaped configuration and folding the side closure forming panels towards one another to an overlapping relationship and securing the side closure panels in the overlapping relationship to form side walls of a bag. The bag forming machine consists of a frame, a former mounted in the frame and a guide means for guiding an unwinding web around the former and drive means for driving the unwinding web around the former. Folding means is provided at opposite sides of the former for engaging the side wall forming portions of a web and folding them inwardly around the former to form closed side walls of a bag.