Grant funds specifically targeted to smallholder farmers to facilitate innovation are a promising agricultural policy instrument. They stimulate smallholders to experiment with improved practices, and to engage with research, extension and business development services providers. However, evidence on impact and effectiveness of these grants is scarce. Partly, because attribution of changes in practices and performance to the grant alone is challenging, and the grant is often invested in innovation processes that benefitted from other support in the past. We discuss three modalities: vouchers, business development matching grants and farmer-driven innovation support funds. Our review points to an important and transversal outcome area of innovation grant systems: the creation of human and social capital to sustain creative thinking and innovative practices. Harmonising measurement on these outcomes could enhance the usefulness and comparability of impact studies and facilitate benchmarking of different policy options for smallholder innovation.