Electromechanical switching devices are grouped broadly into two classes: those which can be used to choose a specific set of contacts from a considerable number of selections, e.g. rotary switches, and those which when operated or released will establish or break the same set of contacts, e.g. relays. Both groups of devices are discussed in considerable detail from the point of view of reliability, and suggestions for maintenance organization are given. A variety of quenching techniques to minimize damage to the contacts are described. Some aspects affecting circuit design are also treated.