The book is made of four lectures. The first is titled "Space and Time in Pre-Relativity Physics". The second lecture is titled The Theory of Special Relativity and discusses the special theory of relativity. The third and fourth lectures cover the general theory of relativity in two parts. Einstein added an appendix to update the book for its second edition, which published in 1945. A second appendix was later added for the fifth edition as well, in 1955, which discusses the nonsymmetric field. The second appendix contains Einstein's attempts at a unified field theory.