This volume contains an extensive presentation of the theory, phenomenology and interpretation of seismic waves produced by natural and artificial sources. Each theoretical topic discussed in the book is presented in a self-contained and mathematically rigorous form, yet without excessive demands on the reader's mathematical background. It is the only book to include such a complete presentation of the mathematical background and modern developments of the WKBJ theory of seismic waves, and detailed discussions of its wide ranging applications. The book will therefore be useful to postgraduate students and research workers specialising in seismic wave theory, theoretical seismology, electromagnetic wave theory and other fields of wave propagation theory.