The new design of image slicer developed at Durham University for 2D area spectroscopy is described. The unit acts as a coupler between the telescope and a spectrograph to reformat a square or rectangular field into a long slit. Its advantages over previous designs of image slicers and other methods using fibers, lenses or narrow-band filtering are discussed, mainly: large field, high spatial resolution, large number of spectral resolution elements, high transmission, and the small size of the instrument. The system is also easy to cool and is then well suited for IR spectroscopy. The proposed design is a new type of image slicer in which the original 2D image is sliced into narrow sub-images that are re-imaged side by side to form a long 1D image at the spectrograph input. The flexibility of the concept at the base of this new design is highlighted through the description of 5 different slicer designs. Three of these are for future instruments now at the design phase: the CGS4 slicer, the UIST slicer and the GNIRS slicer; the two others are studies for possible future slicers on GMOS and NGST. These designs show how easily our slicer can be added to an existing instrument, how it can be incorporated to the slit wheel of future instruments, and how multi-slit reformatting permits a much larger field of view.