Abstract
This paper reviews the history of multipactor discharge theory, focusing on recent models of multipactor accessibility and saturation. Two cases are treated in detail: That of a first-order, two-surface multipactor, and that of a single-surface multipactor on a dielectric. In both cases, susceptibility curves are constructed to indicate the regions of external parameter space where multipactor is likely to occur, taking into account the dependence on surface materials, and the effects of space charge and cavity loading. In the case of a dielectric, multipactor is found to deliver about 1% of the rf power to the surface. The two cases are contrasted in light of experimental observations.