  Semiconductor microcavity systems strongly coupled to quantum wells are now
receiving a great deal of attention because of their ability to efficiently
generate coherent light by the Bose-Einstein condensation (BEC) of an
exciton-polariton gas. Since the exciton polaritons are composite quasi-bosonic
particles, many fundamental features arise from their original constituents,
i.e., electrons, holes and photons. As a result, not only equilibrium phases
typified by the BEC but also nonequilibrium lasing phases can be achieved. In
this contribution, we describe a framework which can treat such equilibrium and
nonequilibrium phases in a unified way.
