This is the first English translation of the book The World as Space and Time written by the great Russian physicist Alexander Friedmann who first showed in 1922 that Einstein's equations have solutions that describe a non-stationary Universe (later the experimental evidence did confirm that the Universe is expanding). The original Russian publication was in 1923. The book is one of the first introductions to the spacetime physics of the theory of relativity for a wider audience. Friedmann had succeeded in both making the book accessible to non-experts and providing rigorous explanations.