Divided into four main sections, this monograph presents the theory of propagation and excitation of volume and surface electromagnetic waves in anisotropic polar and nonpolar conducting crystals, together with the effects of external magnetic and strong electric fields. It also investigates the spectrum of bulk, as well as surface phonon-plasmon polaritons in uniaxial semiconductors, and electromagnetic instabilities leading to the generation and amplification of radiowaves. Additional topics include total transmission, magnon-plasmon polaritons, and the influence of hot 2D carriers. This unparalleled systematic treatment includes novel research on special topics in the field, such as the peculiarities of the polaritons in anisotropic semiconductors in the presence of mobile charge carriers.