Research on plasma physics occupies a prominent place in modern science. It is closely associated with the search for a solution to such extremely important scientific and technical problems as the achievement of controlled nuclear fusion, the development of a magneto-hydrodynamic method for the conversion of thermal energy into electric power, and the conquest of space. In view of the important tasks facing plasma physics and the enormous variety of phenomena with which it is concerned, the intensive development observed in that field during the last two decades was a foregone conclusion. From a branch of physics studying a narrow range of phenomena, plasma physics has turned into a broad, independent avenue of research which is now rapidly encroaching upon and penetrating other branches of physics. The interlinking and interpenetration that exists between plasma physics and related branches of physics is most evident in the realm of theory, since they are based on a common background of method and the inherent unity of fundamental physical laws.