Abstract: The invention concerns expanding files. A flat strip of flexible material (12) is progressively folded longitudinally to form a U-shaped channel. A length of the material equivalent to the developed width of a gusset is drawn forward. A precut partition with glued tabs (113) is placed at the rear of the drawn forward section of material. A fold is formed by pushing the three edges of the channel inwardly. This sequence of operations is repeated to form a multiplicity of pockets, comprising a plurality of parallel partitions joined along three edges to constitute respective filing pockets by the flexible material which is concertina-folded to constitute respective gussets. This multiplicity of pockets may be sectioned to provide separate expanding files. The invention comprises the manufacturing method and the machine for implementing same.