The science of magnetically confined plasmas covers the entire spectrum of physics from classical and relativistic electrodynamics to quantum mechanics. During the last sixty years of research, our initial primitive understanding of plasma physics has made impressive progress thanks to a variety of experiments — from tabletop devices with plasma temperatures of a few thousands of degrees and confinement times of less than 100 microseconds, to large tokamaks with plasma temperatures of up to five hundred million degrees and confinement times approaching one second. We discovered that plasma confinement is impaired by a variety of instabilities leading to turbulent processes with scales ranging from the plasma size to a few millimeters. Understanding these phenomena, which have slowed down progress towards a fusion reactor, requires the use of very sophisticated diagnostic tools, many of which employ electromagnetic waves.The primary objective of this book is to discuss the fundamental physics upon which the application of electromagnetic waves to the study of magnetically confined plasmas is based.