This book is intended for students in the first and second year of university education. It includes the part of the program devoted to the study of the electronic structure of atoms and molecules. In accordance with the spirit of this program, the electronic structure of atoms and molecules is presented in a qualitative way that emphasizes basic concepts and reasoning. All the most elementary notions are introduced gradually, so as to give coherence to the book and make it easy to read. The whole is illustrated with numerous diagrams and figures that greatly facilitate understanding.