One of the major research thrusts of the West African Rice Development Association (WARDA) to meet the ever-increasing demand for rice in West and Central Africa (WCA) has been the development of higher yielding varieties. By 1996 WARDA had developed a range of new interspecific varieties derived from crosses between the Asian rice, Oryza sativa and the African rice O. glaberrima. These varieties, later termed NERICAs (New Rice for Africa), have shown a stable and high yield and tolerance to major biophysical production constraints in a range of upland environments. Their rapid dissemination to small rice farmers in WCA has been achieved through participatory varietal selection (PVS), an applied and adaptive research mechanism in which farmers play an active role in varietal selection, development and spread. PVS lasts for three years during which farmers select and evaluate varieties on their own farms. PVS was initiated in Côte d'Ivoire in 1996 and by 2000 all 17 WARDA member countries had initiated PVS involving 4000 farmers at 105 sites. Particular progress has been made in Guinea where from 1997 to 2000 the number of farmers participating in PVS rose from 116 to 20,000 the area sown to NERICAs from 50 to 8,000 hectares.