One of the serious problems of arcing in relays and switches is leading to material transfer, thus resulting in the loss of contact material and the early end of lifetime. Although this phenomenon has been studied for many years, there are still many unsolved problems. This paper is a review of material transfer due to arcing based on published work by the authors and by the other investigators. Included are a discussion of transfer mechanism, called PSD model (particle sputtering and deposition model); a survey of contact materials, circuit parameters, electrode temperatures, and surrounding gases which have been determined to affect arc behavior and material transfer; the effect of contact surface temperature distribution, arc spot dimension, arc root stability, and arc duration on wearout or loss of contact material from two contacts; and an idea of balance transfer (zero loss) operation. It is expected that this paper could supply some basic considerations for controlling material transfer in practical applications.