Relativity is a foundational concept in physics that addresses the behavior of objects in space and time, particularly under conditions involving high velocities or strong gravitational fields. It comprehends two interconnected theories developed by Albert Einstein: special relativity and general relativity. This book is compiled in such a manner that it will provide in-depth knowledge about the theory and practice of relativity. Also included herein is a detailed explanation of the various concepts and applications of the discipline. In this book, constant effort has been made to make the understanding of the difficult concepts of relativity as easy and informative as possible, for the readers.