The International Centre for Research in Agroforestry (ICRAF) coordinates a research network in the Semi-arid Lowlands of West Africa (SALWA) in four countries: Burkina Faso, Niger, Mali and Senegal. Prosopis africana, an important agroforestry tree species is seriously threatened in this eco-region. ICRAF organized seed collections of this species for long-term conservation and subsequent utilization by small-scale farmers in the West African Sahel. Prior to the collection, ICRAF, the International Plant Genetic Resources Institute (IPGRI) and International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) organized a planning workshop with collaborating national research institutes. Out of this workshop came a consensus on the strategy, logistics and choice of collection sites. To collect as much genetic diversity of P. africana in the SALWA region as possible, 34 collection sites were selected: 15 in Niger, eight in Mali, seven in Burkina Faso and four in Senegal. The main aim of the collection was to capture the genetic diversity within P. africana before the valuable genetic resources are lost. This paper reviews the methodology and results of the germplasm collection.