Various aspects of electron and proton transfer in chemistry and biology are described in this volume. The joint presentation was chosen for two reasons. Rapid electron and proton transfer govern cellular energetics in both the most primitive and higher organisms with photosynthetic and heterotrophic lifestyles. Further, biology has become the area where the various disciplines of science, which were previously diversified, are once again converging. The book begins with a survey of physicochemical principles of electron transfer in the gas and solid phase, with thermodynamic and photochemical driving force. Inner and outer sphere mechanisms and the coupling of electron transfer to nuclear rearrangements are reviewed. These principles are applied to construct artificial photosynthesis, leading to biological electron transfer involving proteins with transition metal and/or organic redox centres. The tuning of the free energy profile on the reaction trajectory through the protein by single amino acids or by the larger ensemble that determines the electrostatic properties of the reaction path is one major issue.Another one is the transformation of one-electron to paired-electron steps with protection against hazardous radical intermediates. The diversity of electron transport systems is represented in various chapters with emphasis on photosynthesis, respiration and nitrogenases. The book will be of interest to scientists in chemistry, physics and the life sciences.