This book introduces the theory of structural dynamics, with focus on civil engineering structures. It presents modern methods of analysis and techniques adaptable to computer programming clearly and easily. The book is ideal as a text for advanced undergraduates or graduate students taking a first course in structural dynamics. It is arranged in such a way that it can be used for a one- or two-semester course, or span the undergraduate and graduate levels. In addition, this book serves the practicing engineer as a primary reference. This book is organized by the type of structural modeling. The author simplifies the subject by presenting a single degree-of-freedom system in the first chapters and then moves to systems with many degrees-of-freedom in the following chapters. Many worked examples/problems are presented to explain the text, and a few computer programs are presented to help better understand the concepts. The book is useful to the research scholars and professional engineers, besides senior undergraduate and postgraduate students.