This text is intended for use in a course in differential equations for student of pure and applied mathematics, the physical sciences, and engineering. The text is designed to be extremely flexible and includes both theory and applications. The text has been written and designed so that the applications can be covered or omitted without a loss of continuity of core topics. The odd-numbered chapters of the book cover the core theory of differential equations with basic applications, while the even-numbered chapters include extended applications from engineering and the physical sciences. In addition, the text includes optional coverage of dynamical systems. Where appropriate, the author has integrated technology into the text, primarily in the exercise sets. Chapters 2, 4, and 6 also include Computing Supplement Sections that are devoted to using numerical methods to solve differential equations.