This book presents a complete theory of ordinary differential equations, with many illustrative examples and interesting exercises. A rigorous treatment is offered with clear proofs for the theoretical results and with detailed solutions for the examples and problems.This book is intended for undergraduate students who major in mathematics and have acquired a prerequisite knowledge of calculus and partly the knowledge of a complex variable, and are now reading advanced calculus and linear algebra. Additionally, the comprehensive coverage of the theory with a wide array of examples and detailed solutions, would appeal to mathematics graduate students and researchers as well as graduate students in majors of other disciplines.As a handy reference, advanced knowledge is provided as well with details developed beyond the basics; optional sections, where main results are extended, offer an understanding of further applications of ordinary differential equations.