  This is a review of strong coupling approaches to grasp the nature of the
phase transition in finite temperature and density QCD. We commence with
classics of the center symmetry and the Polyakov loop in pure gauge theories.
The effective action derived in the strong coupling limit gives qualitatively
plausible behavior for the deconfinement transition at finite temperature. We
can apply the strong coupling analysis to describe the chiral phase transition
with the help of large dimensional expansion. In order to make this article as
self-contained as possible, we elucidate the computational procedure and its
physical meaning in detail. Also the relation between the Polyakov loop
behavior and the chiral dynamics, the phase structure of two-color QCD, and
future possibilities to be pursued in the strong coupling analysis are
discussed.
