In mainland Southeast Asia, the increasing population pressure on montane agroecosystems, their growing integration into the market economies and the impact of national environmental protection policies are provoking rapid transformations in highland farmers' strategies and practices evolving from slash and burn to more intensive, diverse production systems. In such a context, most of the attempts at transferring standard recommended technologies are facing very low rates of adoption. These variable and heterogeneous environments provide opportunities for using holistic systems approaches to address the whole complexity of agricultural development issues. To boost the prospects of significant impact, however, the farmer must be put at the centre of a development-oriented research process. Diagnostic tools at field, farm and watershed levels are used to understand the rapidly increasing diversity of farmers' circumstances, the rationale of farmers' practices and strategies, and key dynamics at work. Such information must be integrated in the research agenda to design improved production systems preserving the resource base while increasing land and labour productivity. At farmers' field level, we use the on-farm agronomic experiment-survey procedure to inventory farmers' techniques, explain their practices and assess their impact on crop function and its environment. In actual farmers' conditions, limiting factors of yields are ranked, yield modelling is carried out, and hypotheses for new cropping systems are derived. At the farming system level, the diversity of farmers' objectives and strategies is analysed and their functioning summarized diagrammatically. Similar farming systems are grouped into a typology and trajectories of evolution displaying the process of accumulation/elimination on the farms along various pathways. Based on results obtained at the two previous scales, the analysis of land-use dynamics at the watershed level spatially distributes the diver