This newly revised fourth edition includes all the latest developments and research work in structural dynamics, making it a truly self-contained book on the analysis and design of structures subjected to dynamic forces or earthquake excitations. It thoroughly and progressively covers every kind of structure, from basic structures modeled as single-degree-of-freedom idealizations to more complex discrete systems and continuous systems with distributed mass and elasticity. To enhance clarity and improve understanding of the material, numerous illustrative and detailed examples are provided. Throughout the textbook use is made of the professional program COSMOS and educational programs in structural dynamics, developed by the author. Bridging the gap between the mathematical formulation of a structural dynamic problem and the ultimate numerical solution given by the computer, this comprehensive resource will be of value to advanced undergraduate and graduate structural engineering students as well as professional structural engineers.