Relativistic heavy ion reactions

In this paper a review of relativistic heavy ion reactions is presented, including results of the new generation of high energy experiments at CERN and Brookhaven. Data on cross sections, secondary particle multiplicities and spectra are discussed, together with the question of applicability of the superposition model and other theoretical models. Some place is also devoted to fragmentation processes (electromagnetic and nuclear) and to hypernuclei which can be effectively studied using relativistic heavy ion beams. The problem of estimation of energy density attained in relativistic heavy ion collisions is treated in more detail in connection with the search for a phase transition to quark-gluon plasma