Quantum fluids of light are many-photon systems that exhibit collective behavior due to effective photon-photon interactions induced by optical nonlinearity. These systems display unique properties, such as superfluid flow around defects, Mach-Cherenkov cones in supersonic flows, and topological excitations like quantized vortices and dark solitons. The review focuses on semiconductor microcavities with strong light-matter coupling, where cavity polaritons act as elementary excitations. The concept applies broadly, including nonlinear crystals, atomic clouds, photonic crystals, and superconducting circuits. The article discusses perspectives for achieving strongly correlated photon gases, including photon blockade, quantum phases in nonlinear cavities, and artificial gauge fields. It covers topics like the driven-dissipative Gross-Pitaevskii equation, superfluid hydrodynamics, dark solitons, and strongly correlated photons. The review highlights experimental observations and theoretical models, emphasizing the non-equilibrium nature of these systems and their potential for novel quantum phenomena.Quantum fluids of light are many-photon systems that exhibit collective behavior due to effective photon-photon interactions induced by optical nonlinearity. These systems display unique properties, such as superfluid flow around defects, Mach-Cherenkov cones in supersonic flows, and topological excitations like quantized vortices and dark solitons. The review focuses on semiconductor microcavities with strong light-matter coupling, where cavity polaritons act as elementary excitations. The concept applies broadly, including nonlinear crystals, atomic clouds, photonic crystals, and superconducting circuits. The article discusses perspectives for achieving strongly correlated photon gases, including photon blockade, quantum phases in nonlinear cavities, and artificial gauge fields. It covers topics like the driven-dissipative Gross-Pitaevskii equation, superfluid hydrodynamics, dark solitons, and strongly correlated photons. The review highlights experimental observations and theoretical models, emphasizing the non-equilibrium nature of these systems and their potential for novel quantum phenomena.