Yam (Dioscorea rotundata and D. cayenensis) is a very ancient traditional crop in West Africa. Farmers' knowledge on this plant is huge especially in Benin where its genetic diversity is important. Farmers' ability to adapt its cultivation and to choose adapted cultivars according to local environment constraints is impressive. In order to record and to understand farmers' knowledge and strategy on varietal management, a survey was carried out in the whole yam belt of Benin. The study covered 70 villages and 13 ethnic groups. More than 300 cultivars (in fact variety names) were recorded. The information was collected using both individual and group interviews. Each variety was characterised for agronomic, post harvest and organoleptic qualities. From the farmers statements it appears that food quality (overall ability to give good pounded yam), yield, earliness, market value, storage ability and seed quality are the major criteria sought by farmers.