Albert Einstein's 1916 book, Relativity: The Special and General Theory, explains his theories of relativity to a non-specialist audience. The book is divided into three parts: Part I introduces the special theory of relativity, focusing on the concepts of space, time, simultaneity, and the constant speed of light. Part II develops the general theory, exploring gravitation as a geometric property of space-time and its implications for the behavior of clocks, measuring rods, and light. Part III considers the universe as a whole, examining cosmological implications and the possibility of a finite yet unbounded universe. The book includes appendices providing further mathematical detail and experimental evidence supporting Einstein's theories.