This study investigated the determinants of the adoption of improved rice??sh farming systems in the Mekong delta to support policy making, agricultural land-use planning and extension of integrated rice??sh farming. Recently these systems have been referred to as adaptations to climate change, while traditional rice??sh systems have often been abandoned. In 2006, we carried out surveys among 94 farmers either practising rice monoculture or having an improved rice??sh 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??sh 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 ?elds and ponds, better access to ?nancial capital and more know-how of rice and ?sh culture and their integration, were more likely to adopt rice??sh systems. Previously identi?ed drivers and factors for adoption, such as an appropriate agro-ecological context and the farmer?s education and training level, were con?rmed. Promoting rice??sh 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.