The phenolic compounds of red wine are separated and isolated by a method involving two precipitations (by EtOH and by MeOH-CHCl2), adsorption of the precipitates and supernatants on to p.v.p., and selective desorption of different fractions by mydroalcoholic and acidic solvents. The method permits the definition of wine composition by groups of phenolic compounds which are identified and quantified, and whose molecular mass is determined. Tanins exist in wine in different forms: combinations with salts (T-S) and with polysaccharides (T-P), highly condensed tanins (TtC), condensed tanins (TC), tanin-anthocyanin complexes (T-A), less condensed tanins (T), procyanidin dimer (P). The combinations of tanins with polysaccharides comprise a new class of compounds whose importance is relatively limited in young wine but increases with time during wine maturation (20 to 30 p. cent of the tanins can exist in this form after 20 years of conservation). The percentage of each class varies in the case of young wine, with the cepage, the level of grape maturaity and the conditions of vinification. During the maturation process, the percentage corresponding to the procyanidin dimer group (P), rapidly attains zero after several years. The tanins of old wines are primarily composed of condensed tanins (TC + TtC) and combinations with polysaccharides and with salts. The anthocyanins exist in wine in 3 forms: free anthocyanins, combined anthocyanins and polymerised anthocyanins which belong to the condensed tanins. The free anthocyanins rapidly dissapear during the first few years of wine maturation. The combined and polymerised anthocyanins generally remain present in regard-less of wine age. These groups play an important role in the determination of wine colour.