This book has benefi ted from the contributions of the African and Brazilian participants attending the APPRI 1 workshop and from the expertise of partners in the European project Agricultural Innovation in Dryland in Africa (AIDA). 2 The contributors to this book represent different sectors of rural development (i.e. research, development, farmer organizations and civil society). Agriculture remains the economic backbone of most African countries, providing almost 70 % of employment. Food shortages, due to recurrent droughts and the fl uctuations in price for edible cereals on the international market, make the rural populations in these regions highly dependent upon the climate and outside aid. The threat of hunger is ever present, especially in the driest regions of Africa (in the arid, subarid and dry subhumid zones), which make up 45 % of the continent’s territory. Agriculture in these regions, identifi ed as Sahelian or Sudano-Sahelian (rainfall between 300 and 800 mm, spread over 4 months), is almost exclusively rainfed. With such limited quantities of water, traditional food crops (millet, sorghum and cowpea), cash crops (mainly cotton) or dual use crops (mainly groundnut and maize) are possible, but rendered extremely vulnerable to the slightest variation in the distribution and amount of rainfall. Market gardening has to contend with wells running dry, while livestock production, usually transhumant, has to cope with drastic reductions in grazing areas. Climate change, low soil fertility and domestic off- take, amplifi ed by population growth, are all factors proven to aggravate the cultural risk.