Our universe can be described mathematically by a simple model developed in 1922 at Petrograd (St Petersburg) by Alexander Friedmann (1888–1925), who predicted that the whole universe would expand and evolve with time before there was any observational evidence. He was an outstanding Soviet physicist, and this vivid biography is set in a wide historical background. The book is a window on the school and university years, military service, teaching and research during a seminal period of Soviet history. The authors include unique archival material, such as Friedmann’s letters from the Front, as well as contemporary records and reminiscences of colleagues. There is a detailed treatment of his work in Theoretical Cosmology (1922–1924), set in the context of the organization of Soviet science at the time.