About two thirds of the forages used by herbivorous livestock comes from diversified (i.e. multi-specific) pastures; these have both agronomical and ecological advantages. An optimal management of such pastures requires a good knowledge of their feeding value. The feeding value of a diversified pasture depends in the first place on the composition of the mixture of species and on the species' feeding value. In grass-legume associations, the proportion of legumes is often determinant for the voluntary intake and the nitrogen value of the herbage. In permanent pastures, the environmental conditions and the type of management determine the botanical composition (especially the types and proportions of grasses with a capture or a conservation strategy, and those of legumes); they thus determine, in a large measure, the feeding value. The value of the voluntary grasses and of the dicotyledons other than the legumes is little known, nor are the interactions among plants on the digestion and intake by the animals. At the scales of the grazing season and of the forage system, the advantage of diversified pastures lies in their greater flexibility of management.