"The 3rd edition is also augmented by two such new chapters: on Nonlocal problems and on Delay functional differential equations. Due to its structure and applications/exercises parts, the book is highly recommended for both undergraduate and graduate studies. Researchers and faculty will also find this book interesting and useful." Zentralblatt MATH Reviews of the Second Edition: "This text would be suitable for courses at the beginning graduate level." MAA Reviews "It is one of the basic books in the field of differential equations, which certainly, will be used by students and specialists in this field. The book is an excellent compound of abstract results and concrete examples, which should prove to be a very popular textbook." Zentralblatt MATH This book presents, in a unitary frame and from a new perspective, the main concepts and results of one of the most fascinating branches of modern mathematics, namely differential equations, and offers the reader another point of view concerning a possible way to approach the problems of existence, uniqueness, approximation, and continuation of the solutions to a Cauchy problem. In addition, it contains simple introductions to some topics which are not usually included in classical textbooks: the exponential formula, conservation laws, generalized solutions, Caratheodory solutions, differential inclusions, variational inequalities, viability, invariance, and gradient systems. In this new edition, some typos have been corrected and two new topics have been added: Delay differential equations and differential equations subjected to nonlocal initial conditions. The bibliography has also been updated and expanded.