  We review the recent developments of the polariton physics in microcavities
featuring the exciton-photon strong coupling at room-temperature, and leading
to the achievement of room-temperature polariton condensates. Such cavities
embed active layers with robust excitons that present a large binding energy
and a large oscillator strength, i.e. wide bandgap inorganic or organic
semiconductors, or organic molecules. These various systems are compared, in
terms of figures of merit and of common features related to their strong
oscillator strength. The various demonstrations of polariton laser are
compared, as well as their condensation phase diagrams. The room-temperature
operation indeed allows a detailed investigation of the thermodynamic and
out-of-equilibrium regimes of the condensation process. The crucial role of the
spatial dynamics of the condensate formation is discussed, as well as the
debated issue of the mechanism of stimulated relaxation from the reservoir to
the condensate under non-resonant excitation. Finally the prospects of
polariton devices are presented.
