In the past few years a new class of solid state optical systems has been developed in which photons have an effective mass and a repulsive interaction between each other. These renormalized photons are known as “polaritons”. One way of looking at this type of system is as an optical medium with world-record nonlinearity, leading to new possibilities for modulating light. Another way of looking at this type of system is as an analogue of a gas of atoms, which can undergo Bose-Einstein condensation and can become superfluid, allowing us to study superfluidity in a new way. I will review the basic experimental methods and recent results of polariton superfluids.