Quark-Gluon Plasma, a state of matter predicted by Quantum Chromodynamics, is expected to be formed in ultra- relativistic heavy ion collisions. In the standard hot Big Bang cosmology, the Universe may have existed in this phase up to about 1 µsec after the initial singularity. The cores of collapsed massive stars may contain QGP. The subject of QGP has thus been a meeting ground of physicists from several sub-disciplines - particle and nuclear physics, statistical physics, astrophysics and cosmology.