AbstractThe physics of vacuum arc cathodes, the advances in their interpretation and the still unsolved problems are summarized. Starting from the experimental experiences the theories of stationary arc spots are described, with their assumptions and variants, their successes and deficiencies. It is shown that an extension of these models by inclusion of non‐stationary processes is inevitable. Such processes are suggested and their importance in a theory of the dynamic arc spot is investigated. Finally the role of surfacecontaminations is discussed, and the general applicability of the vacuum arc models to all kinds of arc electrodes is emphasize