This chapter addresses the physics of radio-frequency (RF) capacitive discharges. It describes various techniques for the excitation of RF field in a gas and the behavior of electrons, the electrodynamic characteristics of discharge plasma and their influence on an oscillating field. In an oscillating electric field, electrons move randomly and simultaneously perform periodic oscillations, which determine much of the RF discharge behavior. The chapter discusses the production and loss of electrons and the plasma maintenance. It provides basic data on the structure and behavior of RF discharges and explains the formation of space charge sheaths at the electrodes and of constant potential in RF plasma. RF discharges can be subdivided into inductive and capacitive discharges differing in the way an RF field is induced in the discharge space. The chapter analyzes a simplified RF discharge model in order to provide a basis for discussion of experimental data.