Microcavity polaritons are half-light, half-matter composite bosons, which are formed in monolithic semiconductor microcavities of the proper design. Recently, Bose-Einstein condensation of polaritons has been reported, that constitutes a new class of quantum fluid out of equilibrium. Unlike cold atoms, superfluid Helium or superconductors, polaritons are in a driven-dissipative situation, and the ...