Structures are often subjected to dynamic forces of one form or the other during their lifetime. This course introduces the theory of dynamic response of structures with emphasis on physical insight into the analytical procedures and with particular application to earthquake engineering. The concepts of structural dynamics are formulated from the first principles of solid mechanics, extending the continuum hypothesis to a numerically efficient finite element approximation. . Forced and free vibration of structures at different levels of idealization such as, continuum formulation, single degree of freedom approximation, and finite degree of freedom approximation, is covered. Special emphasis is placed on the application of the theory in practical earthquake engineering problems. Basic insight into the powerful and efficient frequency domain analysis is provided. Stochastic modelling of earthquake ground motion and structural response is introduced in the framework of theory of stochastic process and random vibration theory. Damping and inelastic modelling concepts are covered in detail.