The book (course notes) is devoted to asymptotic and numerical analysis of point-source radiation in horizontally layered isotropic media with an emphasis on the physics of wave propagation. Includes a detailed discussion of wave phenomena not accounted for by the standard ray theory. Covers material from the second semester of a two-semester seismological course that the author teaches in the Geophysics Department at Colorado School of Mines. 100 pages and 27 figures.