Because of their practical interest, wetting phenomena have been the subject of many experimental and theoretical investigations in the past. However, no coherent description of this field had been obtained until recently. Some intriguing paradoxes remained unsolved. For example, once spreading is achieved, the rate of spreading of a droplet on a solid surface is usually found to be independent of the nature of the solid surface. New theoretical approaches, emphasizing the role of long-range forces, have led to a general framework in which all the experimental observations on spreading harmoniously find their place. The universal laws, experimentally found at the macroscopic level, result from processes occurring on a microscopic scale, typically between 10 and 1000 Å.