The aim of this chapter is to make a presentation of reflectivity experiments on liquid surfaces and interfaces. This is a field where reflectivity techniques are widely used, in particular because the range of available techniques is relatively less important than for solid surfaces (no high-vacuum techniques, no scanning tunneling microscopy, atomic force microscopy is difficult). Reflectivity experiments on liquid surfaces present specific features both experimentally and conceptually. Experimentally, the liquid surface is always horizontal, and therefore requires adapted experimental setups. Morevover, the subtraction of the high background scattering in the bulk liquid phases imposes severe constraints on the experiments.