The monograph is devoted to an important fundamental problem in plasma physics - the reconnection of magnetic lines of force, or "magnetic reconnection," which initiates non-stationary high-energy phenomena both in space and in laboratory conditions. Within the framework of the magnetohydrodynamic approach, theoretical aspects and applications of magnetic reconnection are outlined. The main concepts and processes inherent in magnetic reconnection are consistently considered - the formation of current layers during collapse at the X-type zero point, global three-dimensional magnetic topology with special power lines, various modes and types of reconnection, etc. A description is given of the role of magnetic reconnection in the interpretation of observations and the construction of models of various phenomena on the Sun and in the Earth's magnetosphere, in the acceleration of charged particles. The results of targeted laboratory experiments on the study of magnetic reconnection are presented.