  One of the fundamental questions in the field of subatomic physics is what
happens to matter at extreme densities and temperatures as may have existed in
the first microseconds after the Big Bang and exists, perhaps, in the core of
dense neutron stars. The aim of heavy-ion physics is to collide nuclei at very
high energies and thereby create such a state of matter in the laboratory. The
experimental program started in the 1990's with collisions made available at
the Brookhaven Alternating Gradient Synchrotron (AGS), the CERN Super Proton
Synchrotron (SPS) and continued at the Brookhaven Relativistic Heavy-Ion
Collider (RHIC) with maximum center of mass energies of 4.75, 17.2 and 200 GeV
respectively. Collisions of heavy-ions at the unprecedented energy of 2.76 TeV
have recently become available at the LHC collider at CERN. In this review I
will give a brief introduction to the physics of ultra-relativistic heavy-ion
collisions and discuss the current status of elliptic flow measurements.
