The use of different types of star as background for UV absorption line studies of the interstellar medium (ISM) is reviewed in the context of selected recent investigations of the local interstellar medium (LISM), interstellar gas in general and halo gas. Problems associated with the analysis and interpretation of interstellar absorption lines are highlighted..
The structure of the local interstellar medium is reviewed with emphasis on the new observations of the cold neutral component. The properties of the high latitude molecular clouds are discussed as well as their relationship to the “infrared cirrus” and atomic gas. The molecular clouds are shown to the preferentially along the loops and filaments of local HI gas, but a detailed examination shows the CO and HI peaks are offset from one another. An expansion velocity of 7 km is derived for one of the shells suggesting an expansion energy of - 8 X 10^47 ergs. which is somewhat smaller than that expected for a supernova explosion. If the pressure in the clumps of the high latitude clouds is in equilibrium with the surrounding gas, the pressure in the shells is
10^4-10^5 cm^-3 K, an order of magnitude higher than what is generally argued to exist in the interstellar medium.