An elementary act of charge transfer determines a variety of phenomena in physics, chemistry and biology. The study of charge transfer processes has developed together with general progress in theoretical physics and in fast high resolution spectroscopy, so that research deals now with a broad class of systems, materials and environmental conditions. The specific topics covered are: (1) the environment and reactant-environment interaction at bulk and interfaces; (2) the elementary act of electron and proton transfer; homogeneous and heterogeneous processes; (3) processes of ion and heavy group transfer; ion transport in complex systems; (4) artificially and naturally organized charge transfer in physics, chemistry and biology, technological applications (molecular electronics, sensors, modified electrodes, membrane transport).