The book "Theory of Molecular Excitons" by Aleksandr Sergeevich Davydov is a comprehensive monograph on the theory of molecular excitons. Davydov, a prominent physicist, was a member of the Academy of Sciences of the Ukrainian SSR and a professor at Kiev State University. He is known for predicting "Davydov splitting" in 1948 and for his theoretical investigations into collective excited states of nonspherical nuclei. The book discusses the optical properties of solids, the concept of excitons introduced by Ya. I. Frenkel in 1931, and the progress in the theoretical and experimental study of exciton states. It covers the theory of excitons in molecular, ionic, and semiconductor crystals, as well as in complex organic compounds. The book presents the theory of excitons in the second-quantization representation, the interaction of excitons with phonons and photons, and the dielectric constant of molecular crystals with allowance for lattice vibrations. The monograph includes three recent original papers and provides a detailed mathematical apparatus for the theory of excitons. It discusses the experimental confirmation of exciton states in crystals, exciton luminescence, and the theory of exciton states in different solids. The book also addresses the role of energy-migration processes in solids and biological systems, and the methods for calculating the energy bands of excitons and their interactions with crystal-lattice vibrations. The author hopes that this monograph will contribute to the development of the theory of excitons and the establishment of concepts that best reflect real phenomena. The book is intended for scientists and students specializing in solid state physics. The author thanks several colleagues for their assistance in developing the topics in the monograph. The book is divided into chapters covering various aspects of the theory of molecular excitons, including the fundamentals of the phenomenological theory of electromagnetic waves in dielectric media, the elementary theory of excitons, the theory of exciton states in the second-quantization representation, the interaction of excitons with phonons and photons, and the dielectric constant of molecular crystals with allowance for lattice vibrations.The book "Theory of Molecular Excitons" by Aleksandr Sergeevich Davydov is a comprehensive monograph on the theory of molecular excitons. Davydov, a prominent physicist, was a member of the Academy of Sciences of the Ukrainian SSR and a professor at Kiev State University. He is known for predicting "Davydov splitting" in 1948 and for his theoretical investigations into collective excited states of nonspherical nuclei. The book discusses the optical properties of solids, the concept of excitons introduced by Ya. I. Frenkel in 1931, and the progress in the theoretical and experimental study of exciton states. It covers the theory of excitons in molecular, ionic, and semiconductor crystals, as well as in complex organic compounds. The book presents the theory of excitons in the second-quantization representation, the interaction of excitons with phonons and photons, and the dielectric constant of molecular crystals with allowance for lattice vibrations. The monograph includes three recent original papers and provides a detailed mathematical apparatus for the theory of excitons. It discusses the experimental confirmation of exciton states in crystals, exciton luminescence, and the theory of exciton states in different solids. The book also addresses the role of energy-migration processes in solids and biological systems, and the methods for calculating the energy bands of excitons and their interactions with crystal-lattice vibrations. The author hopes that this monograph will contribute to the development of the theory of excitons and the establishment of concepts that best reflect real phenomena. The book is intended for scientists and students specializing in solid state physics. The author thanks several colleagues for their assistance in developing the topics in the monograph. The book is divided into chapters covering various aspects of the theory of molecular excitons, including the fundamentals of the phenomenological theory of electromagnetic waves in dielectric media, the elementary theory of excitons, the theory of exciton states in the second-quantization representation, the interaction of excitons with phonons and photons, and the dielectric constant of molecular crystals with allowance for lattice vibrations.