Observational data and studies on material in the galactic system are reviewed. Mechanisms of radio emission are discussed relative to thermal radiation, synchrotron radiation, and the existence of non-thermal radiation. Observational data on the shell and the inner part of the Crab nebula are considered along with properties such as synchrotron radiation, energy spectrum, magnetic fields, and force-free fields, The temperature and motion of an interstellar gas observational evidence of interstellar magnetic fields are discussed. Interstellar plasma is discussed relative to magnetic fields, the expanding motion near the galactic nucleus, halo theories, and the energy budget of the interstellar gas as a whole. (C.J.G.)