In Soudano-Sahelian areas the main feature of the climate is the very important inter-annual and intra-seasonal rainfall variability which is synonymous of risk and uncertainty for rainfed staple crops. That explains why fanners didn't adopt intensification oriented recommendations, still preferring extensive strategies based on traditional rustic and limited yield varieties and low investrnents. However population growth and international food-crops markets are stressing the situation. In this context agricultural insurances could be a solution to help famers to cope with bad yields, thus keeping them motivated to invest. Among insurance systems, weather index based ones seem attractive because they are operational and cheap since the payouts are linked to observed climatic data, allowing saving damage assessment. In recent years they have been successfully proposed to small farmers in different under-development countries such as India, Malawi, Thailand, Ethiopia, Mexico, etc. The presented study was conducted in three areas of Senegal (Nioro, Kaffiine and Gossas, where average annual rainfalls are respectively 709, 600 and 501 mm on the 1970-2007 period) to assess the feasibility of a rainfall index based insurance (RIBI) for groundnut producers and define its technical and economical parameters. Agronomical and agrometeorological data and concepts and the crop water balance model SARRABIL©CIRAD were used to assess the ranges of the technical parameters. Socio-economical surveys provided the required economical data. Last, simulations and expertise integrating ail the elements allowed designing the terms of the insurance con tracts. The study indicates there is an opportunity for RIBI development in Nioro and Kaffrine areas, but outlined the potential limits of this tool in areas such as Gossas where rainfalls ranges between 450 and 550 mm, except considering public subsides. lt also indicated that otlicial aggregated yields data are not sui table to calibrate su