ASTR 542 is a graduate level course that covers the physics of the interstellar medium (ISM) and emission nebulae such as H II regions, supernova remnants, and planetary nebulae. We will study all the important emission mechanisms, including recombination, ionization, and collisional heating and cooling that operate in the ISM. The course will show why the ISM segregates into its various phases, discuss fluid dynamics of supersonic flows, and consider plasma processes of interest to astronomers. All of these subjects will be discussed in the context of recent ISM discoveries, many made possible with new images and spectra taken with the Hubble Space Telescope, Spitzer, and other satellites. Students should have completed the Astrophysics I class (ASTR 451/551) or its equivalent. Having had Radiative Processes, PHYS 541, is also useful, but that course not strictly a prerequisite.