After recalling the early stages of quantum chemistry, a more detailed and systematic description of the post-war period (approx. 1945-1960) follows. The essential features of both p-electron and s-electron eras are described: the simplest versions as well as procedures including electron repulsion are considered. Then attention is paid to valence and Rydberg excited states. The review is closed by remarks on hydrogen bonds and other weak intermolecular interactions.