Introduction: Corrosion can be generally defined as degradation of materials in a reaction between the material and its environment. The nature of the reactions leading to degradation depends on the class of materials: for metals, corrosion is an electrochemical process, whereas ceramics can fail by purely chemical dissolution. This article mainly discusses the corrosion processes of metallic materials, that is, electrochemical corrosion reactions. First, the thermodynamic and kinetic principles of electrochemical corrosion reactions are introduced, followed by a section on metals passivity. The most relevant modes of corrosion processes are briefly described. Physical–chemical principles of corrosion protection are described. At the end, selected examples of corrosion phenomena encountered in electrochemical power sources are briefly discussed...