[en] A paper published by Einstein in 1917 was intended primarily to be a record of the thinking by which he had discovered much of the true nature of general relativity but it is now regarded as the starting point of the modern science of mathematical cosmology. The development of relativistic cosmology over the past 60 years which has produced fundamental insight into the physical history of the Universe and of the nature of physical science itself is examined. The concepts of curved space-time, Mach's principle and the cosmical constant, are considered. (U.K.)