Guinea yams (Dioscorea cayenensis Lam. D. rotundata Poir) have been described several times as resulting from a process of domestication of wild yams of the Enantiophyllum section, initially by Burkill (1939) and by Miege (1952) and later, on a more elaborated way, by Hamon (1987) and Terauchi et ai. (1992). It is only recently that research institutions realized that the domestication of wild yam is still an active process. The first attempt to clarify the techniques of domestication used by the African farmers in West Africa was conducted in 1995 in northern Benin within the Bariba ethnic group (Dumont and Vernier, 2000). In order to obtain more global vision of yam domestication the same study was extended to other yam grower ethnic groups in Benin and Nigeria.