Prospective analysis using farming systems modelling helps explore farmers' strategies and create scenarios in different contexts such as pioneer zones, rehabilitation areas or traditional tree-crop belts in the humid tropics and in a new context of globalisation, decentralisation and market uncertainty. Combined with social and historical analysis, economic modelling contributes to building better and more suitable alternatives in terms of decision-making processes in partnership with both farmers and developers. This approach helps farmers to make the right decision at the right time concerning their future investments, in particular when tree-crops are involved. CIRAD/INRA/IAMM developed a software called "Olympe" that enables modelling of farming systems as well as farming groups. Use of this software aims to improve farmers' understanding of their own situation and of their actual socio-economic context and also provides orientations for agricultural and development policies for institutions or donors. Prospective analysis enables the creation of scenarios of potential farm pathways that can be used in the definition of agricultural policies, recommendations and to measure the likely impacts of such policies so they can be adapted to the real situation faced by farmers. In this paper, a comparison between the situations of rubber farmers in Indonesia and Cambodia illustrates this approach.