The reader's proposed translation of Herzberg's "Molecular Spectra and Molecular Structure, I. Diatomic Molecules" provides a comprehensive view of diatomic molecules in terms of their energy and spectroscopy. This book is a useful guide in processing experimental data and deciphering molecular spectra. A large number of examples, diagrams and diagrams makes it easy to navigate in various questions regarding certain features of the structure of spectra, which are considered in the book from the point of view of an experimenter, spectroscopist-practitioner.