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A summary will be given of the principal new insights obtained so far with HST concerning the origin and physics of the objects responsible for the absorption lines observed in QSO spectra. These include 1) the incidence and nature of the Lymam alpha clouds observed at redshifts below $z \sim 1.5$, 2) the observation of the Gunn-Peterson effect in He~II, 3) the search for absorption in voids in the distribution of galaxies, 4) the nature and evolution of the galaxies responsable for the heavy element lines such as C~IV and Mg~II, 5) absorption lines due to thr halo of our Galaxy, and 6) the broad absorption lines due to outflows from certain QSOs. A report on the current status of the HST ``Key Project'' on QSO absorption lines will also be given.
