This chapter contains sections titled: General Characteristics Classification of Redox Reactions Characterization of Mechanism Outer Sphere Reactions The Applications of the Marcus Expression Inner Sphere Redox Reactions The Bridging Ligand in Inner-Sphere Redox Reactions Some Other Features of Redox Reactions Mixed Outer- and Inner-Sphere Reactions Two-Electron Transfer Redox Catalyzed Substitution Stereoselectivity Intramolecular Electron Transfer Between Two Metal Centers Metal Complexes with Reducible Ligands Induced Electron Transfer Electron Transfer in Proteins The Future