The effect of polydispersity on liquid-liquid phase relationships in equilibrium is reviewed and found to be similar for all the kinds of systems examined. As a rule, it is not allowed to identify a cloud-point curve with a binodal (coexistence curve), nor the maximum in a cloud-point curve with a critical point. In any kind of system (solvent-polymer; polymer 1-polymer 2; solvent-non-solvent-polymer; solvent-polymer 1-polymer 2) measurement of the consolute state opens the way towards accurate determination of interactions parameters. Use of the critical opalescence for the latter purpose is subject to complications.