Abstract: Sheet stacking apparatus for handing simplex and duplex copy sheets has both inverting and non-inverting copy sheet paths (6a, 6b) which can be selected by moving a diverter (7) between two positions. In one position (7a) the copy sheet is directed along guide branch (6a) into slots (9) of the disc inverter (8) which rotates to invert the sheet. The sheet is advanced by nip rolls (32a, 32b) at the output end of the inverting path (6a). An upwardly inclined collection tray (10) has a backstop (30) located in the path of the inverted sheet, but with recesses (20) which allow the discs (8) to pass freely. The lead edge of the sheet is brought to rest when it abuts the backstop (30). Nip rolls (32a, 32b) continue to advance the sheet until its trail edge exits the rolls (32a, 32b) and thus it is delivered into the collection tray (10) inverted.