The theory of relativity incorporates the special theory of relativity and the general theory of relativity. Special relativity explains the relationship between space and time, and applies to all physical phenomena in the absence of gravity. General relativity describes the law of gravity and its relation to other natural forces. It is applied in the fields of cosmology and astrophysics. The theory of relativity revolutionized theoretical physics and astronomy. Some of the concepts which are studied within this discipline are space-time, relativity of simultaneity, kinematic and gravitational time dilation, and length contraction. This book consists of contributions made by international experts. Different approaches, evaluations, methodologies and advanced studies on relativity have been included herein. The book aims to equip students and experts with the advanced topics and upcoming concepts in this area.