For some time now there has been an interest in the nop. Β linear interaction of electromagnetic waves in plasma [1,2]. But only in the last few years has the theory of nonlinear wave interΒ action effects undergone such vigorous development as to result in the formulation of clear phYSical concepts regarding the mechΒ anisms of interaction. This development has been engendered by attempts to solve many of the plasma-physical problems accomΒ panying the tremendous growth of experimental research [3]. The importance of nonlinear effects in modern plasma physics is disΒ cussed in detail in Chap. I. At this point we merely stress the fact that today the analysis of nonlinear effects is a practical neΒ cessity in any experiment involving plasma instabilities. We should also point out that plasma instabilities can assert themΒ selves extensively in solids (solid state plasma) and play an imΒ portant part in the study of cosmic plasma. Consequently, the problems of nonlinear wave interaction in plasma are of concern to those working in widely different areas of physics. Yet it is difficult to assimilate the results of investigations on nonlinear effects, owing to the complicated way in which the results of origΒ inal research are presented. In the present book the author hopes in some measure to fill the need for a text on the physics of nonΒ linear effects that is accessible to a fairly general audience.