This book highlights a systematic introduction to the basic theory of elastic wave propagation in complex media. The theory of elastic waves is widely used in fields such as geophysical exploration, seismic survey, medical ultrasound imaging, nondestructive testing of materials and structures, phononic crystals, metamaterials and structure health monitoring. To help readers develop a systematic grasp of the basic theory, and thus its applications, the book elaborates on the theory of elastic wave propagation in isotropic solid media, covering phenomena in infinite media, interfaces, layered structure with finite thickness, Rayleigh wave and Love wave propagating along the surface of semi-infinite solid and covering layer, and the guided waves and leaky waves in flat plates and in cylindrical rods. The propagation patterns and features of guided waves in cylindrical shells and spherical shells are also introduced. The author wrote the book based on a decade of teaching experience of a graduate course of the same name and two decades of research on the theory and applications. The book is a valuable reference for students, researchers and professionals who expect an understandable and comprehensive discussion of the theory, analytical methods and related research results.