This working paper describes the Decision Analysis work done on the Drylands Development Programme (DryDev) in Sub-Saharan Africa. The programme was designed to address water management, food security and rural economic development in the drylands of Kenya, Ethiopia, Burkina Faso, Mali and Niger. The initiative was geared towards supporting the transition of smallholder households from subsistence farming and reliance on emergency aid towards more sustainable agribusiness enterprises. Decision Analysis was used as a quantitative ex-ante impact assessment tool to prioritize interventions based on their projected impacts. The assessment simulated the potential of four interventions in six project sites of Eastern Kenya, incorporating risk and uncertainty in decision modelling. The result delivered to the decision makers was a range of plausible outcomes from a cost benefit analysis and a description of the variables with the highest critical uncertainties whose measurement would most facilitate decision-making. This paper describes the modelling process, which was both participatory and probabilistic, for each intervention. It gives details on the quantitative approach used for each of the four interventions separately, highlighting the benefit, cost and risk variables and the interactions between them. It then discusses the results of each decision model and from these makes recommendations to the decision makers. The penultimate section highlights the limitations and constraints faced by the analysis, and this is followed by general conclusions. The DryDev Programme is funded by the Netherlands’ Ministry of Foreign Affairs, with ICRAF as the lead implementing agency and SNV, CARITAS, ADRA and World Vision as implementing partners.