This tutorial describes the physical principles and mechanisms that determine the behavior of liquid and solid dielectrics when exposed to powerful voltage pulses. The phenomenon of dielectric breakdown has found wide application in pulsed energy, in particular, on its basis, thrusters for spacecraft have been created. The rapid development of technology, the increase in the power of devices and the expansion of the field of application of electrical breakdown led to the use of new materials in high voltage technology. At the same time, the behavior of many classical dielectrics when powerful pulses of several nanoseconds are applied to them is not fully known.