This paper is a review of vacuum-arc phenomena which are related to switching devices. Despite the device overtones, the approach adopted for this paper is fundamental. Topics discussed include the drawn arc, the triggered arc, the power input to the cathode spot, cathode-spot division, arc stability, substructure of the cathode spot, dielectric recovery processes, and breakdown between electrodes subjected to repeated arcing. Frequent reference to the recent literature is made. Due to the somewhat specialized nature of certain parts of the discussion, introductory and appended sections of the paper present supplementary remarks on the concept of plasma and electrical conduction in gases, electron emission processes, and electrical contact phenomena.