The branch of pure mathematics that is dedicated to study of integers is called number theory or arithmetic. Number theory studies the properties of prime numbers, rational numbers, and algebraic integers. This book elucidates the concepts and innovative models around prospective developments with respect to number theory. Such selected concepts that redefine this subject have been presented in it. It will provide comprehensive knowledge to the readers. Those in search of information to further their knowledge will be greatly assisted by this textbook. Coherent flow of topics, student-friendly language and extensive use of examples make this book an invaluable source of information.