Journal article: International agricultural research is often motivated by the potential benefits it could bring to smallholder farmers in developing countries. A recent experimental literature has emerged on why innovations resulting from such research, which often focuses on yield enhancement, fail to be adopted due to either external or internal constraints. This article reviews this literature, focusing on the traits of the different technologies and their complexity and distinguishing between yield-enhancing, variance-reducing, and water- or labor-reducing technologies. It also discusses how farmers’ reallocation of inputs and investments when external constraints are lifted suggests that they often do not seek to increase yield or input intensity. The article further reviews evidence indicating that a technology's potential as observed in agronomical trials is not necessarily a good predictor for smallholder farmers’ demands for the technology in real-life conditions. The last section derives conclusions for the research and policy agenda.