This book "Number Theory for Olympiads" presents the interesting world of numbers in a playful manner. Crafted especially for the students of classes 7 to 12, this book will be useful for various examinations such as Mathematics Olympiads, school exams, board exams, etc. Even, certain concepts are discussed for examinations like JEE Main & Advanced. Number theory is an essential part of mathematics courses at the undergraduate level. Therefore, this book can also serve as an introductory course in Number theory at the undergraduate level. The features included in this book are: A sufficient number of examples and illustrations are given to explain the concepts The chapter 'Key Concepts & Results of Number Theory' summarizes all the key concepts The chapter "Olympiad Problems" consists of a wide range of problems from the previous year's questions of various regional, national, & international mathematics Olympiad Certain concepts are discussed for JEE Main & Advanced