This study investigated the determinants of the adoption of improved rice–fish farming systems in the Mekong delta to support policy making, agricultural land-use planning and extension of integrated rice–fish farming. Recently these systems have been referred to as adaptations to climate change, while traditional rice–fish systems have often been abandoned. In 2006, we carried out surveys among 94 farmers either practising rice monoculture or having an improved rice–fish system. We analysed data among others with binary logistic regression and simulated adoption by using fuzzy logic. Per capita and per hectare incomes of households practising rice–fish systems were nearly double, while their farm size was 1.3 times larger than that of the rice monoculture farms. Households with larger homesteads, i.e. neighbouring irrigated fields and ponds, better access to financial capital and more know-how of rice and fish culture and their integration, were more likely to adopt rice–fish systems. Previously identified drivers and factors for adoption, such as an appropriate agro-ecological context and the farmer’s education and training level, were confirmed. Promoting rice–fish systems needs participatory extension and research approaches for sustainable agriculture strategies such as integrated pest management (IPM) in which farmers, trainers and researchers optimize technologies in constantly changing contexts.