The book is devoted to the discussion of modern aspects of the theory of hadronic matter under extreme conditions. It consists of 12 selected contributions to the second international workshop on this topic held in fall 2019 at JINR Dubna, Russia. Of particular value are the contributions to lattice gauge theory studies attacking the problem of simulating QCD at finite baryon densities, one of the major challenges at the present time in this field. Another unique aspect is provided by the discussion of puzzling effects that appear in the poduction of hadrons in nuclear collisions, like the horn in the K+/pi+ ratio, which are subject to hydrodynamic and reaction-kinetic modeling of these nonequilibrium phenomena.