Quasar Absorption Lines and the Intergalactic Medium
  The importance of HST for the study of quasar absorption lines and of the nature of the intergalactic medium is illustrated by reviewing selected results from past HST observations. Topics reviewed include the study of Ly-alpha absorbers at low redshift and the search for a diffuse IGM at high redshifts. 
Buell T. Jannuzi (NOAO)