The book reviews the results of studies on the pulsed breakdown in gases of elevated pressure and gives the present notion of the physical processes accompanying the discharge formation and operation. The Townsend and the streamer breakdown mechanisms are discussed. Much attention is given to the self-sustained space discharges initiated by UV radiation and to the discharges in gases ionized by a fast electron beam. The book is addressed to researchers and engineers engaged in the gas discharge physics and in the utilization of this type of discharge in lasers, switches and other devices.