The book is devoted to the phenomenon of explosive electron emission (EEE) discovered by the author and his co-workers in 1966. This emission results from microexplosions which occur at the surface of a cathode in the event that a high energy has been concentrated in microvolumes at the surface. Electrons are emitted as discrete bunches, ectons, as termed by the author. The book covers the properties of the cathode plasma and the liquid metal at the cathode, the material removal from the cathode, the microrelief of the cathode surface, the drop fraction of the cathode erosion products, the current-voltage characteristic of a diode, and the processes at the anode initiated by the electron current of EEE. In conclusion, three most-used types of vacuum diodes depending for their operation on EEE are described. These are diodes producing broad stripwise beams, cylindrical beams, and high-current self-focusing beams. The book is addressed to engineers engaged in pulsed power and involved in the development of high-power gas lasers, vacuum switches, high-current electron and ion accelerators, high-power pulsed X-ray apparatus, etc. and to physicists concerned with vacuum breakdown, electron emission, and intense charged-particle beam problems.