In this landmark work, Albert Einstein presents the principles of special and general relativity in a form intended for readers without advanced mathematical training. He explains how space, time, motion, gravity, and the speed of light are connected, challenging traditional ideas of an absolute universe. Through clear reasoning and carefully developed examples, Einstein reveals how measurements of time and distance depend upon the observer’s motion and how gravity emerges from the structure of spacetime. Both scientifically important and intellectually fascinating, the book offers an accessible introduction to one of the most revolutionary theories in modern physics.