Continuing interest in sustainable biofuel production is linked with sustainable farming and begs for insights from farming systems research on sustainability assessment and the role of family farms. The aims of this work were two-fold. First, to present a tools and methods selection framework supporting indicator-based sustainability assessment. Second, to apply the framework to the case of castor beans (Ricinus communis L.), family farmers and the biodiesel industry in the southeast of Brazil. The framework synthesizes existing work on sustainability assessment within the agricultural domain. Transparent selection of tools and methods is supported by sequentially accounting for the context of sustainability, dealing with space, classifying the ‘nature of research’ and the degree of integration of different facets of sustainability. The framework is demonstrated with an exploratory assessment of the potential for castor bean cultivation within the current farm type of extensive pasture and fodder crops for dairy cattle. The study accounted for the range of productivity levels within the current farm type and for different management decisions when including castor beans. Assessment was made against economic development, livelihood stability and soil fertility criteria. Selected tools and methods included farm surveys, alternative farming system design and input–output calculations. The results demonstrate the greatest opportunity for castor bean cultivation by currently low productive farms. There is a trade-off of income derived from milk production that is supported by fodder production, and income from castor beans. Decisions regarding areal extent of castor beans and supplementing animal feed, are shown to be farm-specific, and depend upon the interactions between current farm productivity and prioritisation of sustainability criteria. However, generally it is shown that castor bean cultivation should be linked to animal production so that current risk management and income levels can be supported and improved. Further, to maintain soil fertility, castor bean cultivation with nitrogen inputs is necessary. The cyclic nature of the framework supports the next contextualisation of the sustainability question. For our application, constructive future work in a next cycle could include extending to regional level and accounting for temporal variability. --------------------------------------------------------------------------------