The interest in biodiesel as an alternative fuel is ever increasing due to recent legislation requiring fuel manufacturers to add a set percentage of biofuel in their products. The present EU's biofuel policy introduces a blending target involving reaching a mandatory 6% reduction in the greenhouse gas intensity of fuels by 2020. Thus, biodiesel production that is sustainable in terms of feedstock, as well as of employment of clean, safe, and efficient manufacturing processes, is becoming urgent. In the past decade, many industrial processes have shifted toward the use of solid acid catalysts as a ‘green tool’ to replace traditional catalytic systems to efficiently produce biodiesel from low-cost biomass feedstock, i.e., resources with high free fatty acid content. Heterogeneous systems, indeed, enable their easy separation and recovery, recycling and reuse, possibly leading to waste-minimized protocols. Moreover, there is an ever-growing interest in exploiting the synergy between heterogeneous catalysis and continuous flow technology as a viable integrated sustainable solution to process intensification. In this chapter, we focus on the recent advances in the use of tuneable and versatile organic polymer-supported solid acid catalysts to produce biodiesel fuel in batch and in continuous mode. We restrict the discussion to the most widely employed members of this class, i.e., cation-exchange resins. Trends are identified between physico-chemical and morphological properties of the catalysts and their performance, while their recyclability aspects are also examined. Finally, a survey and brief discussion on these catalysts' performance in batch and continuous flow production of levulinates – biofuel additives structurally related to biodiesel – are also provided.