Republication of: The beginning of the world from the point of view of quantum theory

This is a reprinting of a very short note by Georges Lemaitre, first published in Nature in 1931, in which he envisages the Universe evolving out of a single atom by quantum processes. The paper has been selected by the Editors of General Relativity and Gravitation for re-publication in the Golden Oldies series of the journal. This republication is accompanied by an editorial note written by Jean-Pierre Luminet.