  In the recent years we have learned that light quarks play a crucial role in
QCD-like theories, transforming it to many different phases. We review what is
known about them, both from lattice and non-lattice approaches. A particularly
simple mechanism of the QCD chiral restoration phase transition is discussed
first: it suggests that it is a transition from randomly placed tunneling
events (instantons) at low T to strongly localized tunneling-anti-tunneling
pairs at high T. Many features of the transition found on the lattice can be
explained in this simple picture. Very relevant for RHIC, this approach
predicts a strong non-perturbative interaction between quarks $above$ the phase
transition. It also predicts that QGP-like phase sets in at $zero$ temperature,
provided few more light quark flavors are added to QCD. Finally, we also
discuss possible experimental signatures of the QCD phase transition. One issue
is CERN dilepton data, possibly related with ``dropping'' masses of $\rho, A_1$
mesons. Another is direct manifestation of a $softeness$ of EOS (smallness of
pressure/energy density) in the phase transition region in flow and even the
global lifetime of the system.
