This book is an introduction to the study of Diophantine equations. The book, organized in two parts, introduces the reader to the main elementary methods necessary in solving Diophantine equations, presents some classical Diophantine equations, and contains complete solutions to all of the exercises. The book is intended for undergraduates, high school students and their teachers, mathematics contests participants (including Olympiad and Putnam competitors), as well as any person interested in essential mathematics. This work uniquely presents unconventional and non-routine examples, ideas, and techniques.