Summary: THE scope of this little work, based on four lectures, is, as explained in the author's preface, to present, as simply and shortly as possible, quantum physical theory having an interest to chemists, and avoiding any use of mathematics. As the limitations imposed by these conditions indicate, the book is a résumé of the position (in 1929), popular only to the extent of being written for the non-specialising scientific worker. The four chapters deal with the arithmetic of chemical periodicity, the quantum theory of valency and chemical forces, electron grouping and the periodic system, and the quantum problem of molecular and nuclear structure. An English version has appeared under the title of “Quantum Chemistry”.