Around 1900, R. F. Earhart, a graduate student working with A. A. Michelson, used an interferometer to establish that voltage breakdown could occur at a predetermined surface field, rather than through an electron avalanche. The first simple explanation of this data was given by Lord Kelvin about three years later. In spite of this early progress, the field of vacuum breakdown is still not settled science, and it has recently been said that we may never understand this physics. After a review of the history and important questions involved, we describe a self-consistent model of rf breakdown that seems to provide useful answers to a wide variety of questions. We compare our model with mechanisms proposed by others to explain breakdown and the surface damage it produces, and we describe a variety of possible experiments to further improve our understanding.