... NICS will be the only infrared instrument for the first light of the TNG; as a consequence, we decided to incorporate a sufficient degree of operation flexibility by providing the instrument with six different observing modes, three aimed at imaging and three at spectroscopy: . ... It will be possible to use the narrow band filters as order sorters; this will allow to perform high resolution long-slit spectroscopy in the wavelength ranges covered by the available narrow band filters. ...