"The Physics of Atoms and Quanta" is presented here in its fourth edition which is now identical with the 5th German edition. It is written primarily for undergraduates in physics and chemistry: the student will find here a total of 160 problems and their solutions. This textbook gives a unique introduction to both experiments and theory in this field. Recent developments have been included, and the book is therefore also directed at active researchers needing an up-to-date reference book.