Extreme states arise when a substance is exposed to powerful shock, detonation and electric explosive waves, concentrated laser radiation, electron and ion beams, during powerful chemical and nuclear explosions, hypersonic motion of bodies in dense planetary atmospheres, high-speed impact, and in many other situations characterized by extremely high pressures and temperatures. The study of matter under extreme conditions is one of the most urgent and intensively developing fundamental scientific disciplines, located at the intersection of plasma physics, nonlinear optics, condensed state, nuclear, atomic and molecular physics, and relativistic and magnetic hydrodynamics. In our country, research in the field of physics of high energy density and extreme states of matter is dynamically developing thanks to the active cooperation of the Russian Academy of Sciences and the Rosatom State Atomic Energy Corporation.