Crop-based biofuels represent an environmental and political alternative to fossil fuels, as well as an important source of rural development income; as global biofuel markets continue to mature, however, their impact on food security remains controversial. This study investigates the effects of biofuel feedstock adoption by smallholders in the northwestern Cambodian province of Banteay Meanchey, a region undergoing rapid land use change following the formal end of the Khmer Rouge era in 1989 and subsequent rural resettlement. Remote sensing data combined with field interviews pointed to three discrete phases of land use change in this period: first, as a result of the establishment of new settlements (mainly subsistence rice production); second, via the expansion of cash crop cultivation into forested areas (mainly grown on upland fields); and third, due to the response of smallholders to a sharp increase in regional demand for cassava starch (grown exclusively on upland fields). The study found that agricultural expansion due to cassava growing was severe, but it was not the sole contributor to deforestation in the region. The exposure of smallholder economies to the volatile cassava market had severe consequences for livelihoods and food security. The paper concludes with a discussion of the probable impacts of the emerging cassava market on trajectories in land use, land ownership, and land access in rural Cambodia. The case looks at biofuel adoption in the context of other land use changes, but also provides evidence at the local scale of how a strongly market driven crop, in this case biofuel feedstock, can have striking environmental and socioeconomic consequences.