I am somewhat embarrassed to discuss ST observations of the inter-stellar medium (ISM) of our own Galaxy for two reasons. First of all itseems, at least at the moment, a less exciting subject for the ST thansome others. Secondly, I sadly found, while reading the literature inpreparation for this discussion, that I am not sufficiently familiarwith optical astronomy to be able to guess where the real advances willcome. As a consequence I shall merely summarize (a selection of) observations that have already been proposed, including some for the ISM inexternal galaxies. Unless otherwise stated, all observations for thehigh resolution spectograph (HRS) and the faint object spectograph (FOS)are described in more detail by Brandt et al (1977) and by Harms et al(1977), respectively. Observations for the wide field camera (WFC) andfaint object camera (FOC), on the other hand, were already discussed atlength at the ESA/ESO Workshop on “Astronomical Uses of the Space Telescope” and I shall refer to review papers in the workshop proceedings.