For years the Saas-Fee advanced courses have been greatly appreciated and highly regarded by astrophysicists and astronomers. In a form accessible to students this volume discusses interstellar matter, including the most recent theoretical and observational results.

Distribution and Observational Properties of the ISM.- Observations of HI and Other Tracers of the Low-Latitude Morphology of the Interstellar Medium in Our Galaxy.- Galactic Rotation and the Constants Specifying the Kinematic and Linear Scales of the Milky Way; Line-broadening Mechanisms Determining Profile Shapes at Low Latitudes.- Global Structural Distribution of Low-Latitude Tracers of the Inner Galaxy.- Comparative Global Properties of Interstellar Dust and Gas in the Galaxy.- Kinematics and Distribution of Neutral Interstellar Gas in the Galactic Bulge Region.- The Warped and Flaring Layer of Atomic and Molecular Gas in the Outer Galaxy.- Large Scale Dynamics of the Interstellar Medium.- Basic State of the Interstellar Gas.- Large Scale Heating and Cooling.- Explosions.- Gas Flow in Spiral Density Waves.- Gas Instabilities.- Global Star Formation.- Physics and Chemistry of Molecular Clouds.- Tools of Infrared and Radio Astronomy.- Heating and Cooling Processes.- Interstellar Chemistry.- Structure and Dynamics of Molecular Clouds.- Circumstellar Clouds and Masers.- Molecular Clouds in the Galactic Center and External Galaxies.