Great discoveries in the history of physics have frequently been associated with measurements of matter under extreme conditions. The physics of small size and energy requires quantum mechanical principles, while the physics at high velocity requires special relativity. Recent experimental studies of the high energy central heavy ion collisions at CERN indicated closing to another exciting threshold: deconfinement and chiral symmetry restoration in nuclear matter at superhigh energy density. Calculations, using the Quantum ChromoDynamics (QCD), predict that at sufficient temperature and density hadronic matter will undergo a phase transition in which bound quark systems become locally unbound yielding a new phase of matter, the Quark-Gluon Plasma (QGP). Deconfined quark matter has not been seen since the first few microseconds following the Big Bang. Investigations of this new Quark-Gluon Plasma state are listed in the Long-Range Plan for Nuclear Physics as the highest priority. The recently completed RHIC accelerator is aimed to enter this new regime by creating collisions of the gold ion beams, each with energy 100 A GeV. As it follows from numerous theoretical predictions the energy of collision in this case should be more than sufficient to surpass the phase boundary. The principle goal of the PHENIX,   STAR,  PHOBOS and BRAHMS experiments at RHIC is the discovery and characterization of the Quark-Gluon Plasma. During the first three years of RHIC operation a huge amount of data is accumulated. According to the preliminary analysis the energy density higher than 5 GeV/fm**3 was produced in central gold-gold collisions at RHIC. This essentially exceeds the upper limit found from the previous experiments at SPS. Although it is generally believed that the deconfined state of nuclear matter can be created already at the RHIC energies, the detailed investigations of this exciting phenomenon will be realized at higher energies at Large Hadron Collider at CERN where operation of ALICE detector is scheduled on 2007.