In this Chapter, we give a brief review of the state of the art of theoretical and experimental studies of quantum fluids of light. Such systems consist of ensembles of photons that acquire a finite mass from spatial confinement or diffraction and finite binary interactions from the optical nonlinearity of the optical medium. The peculiar properties of these fluids are highlighted in comparison with standard condensed matter systems, with a special emphasis on the novel possibilities that they offer for the generation, the manipulation and the diagnostics of the fluid, as well as on their intrinsically non-equilibrium and/or dynamical nature. Perspectives towards a new generation of experiments on strongly correlated fluids of light and towards opto-electronic applications are finally sketched.