The success and social/environmental impact of a challenge fund depends on: additionality (i.e. serving companies that could not access commercial finance), positive externalities (i.e. the selection of projects with the highest potential development benefit), and systemic impact (i.e. driven by demonstration/imitation effects and the creation of new markets). Development Informatics working paper no. Infrastructure public-private partnerships in the developing world: Lessons from recent experience", The Journal of Development Studies, 51(4), 335-354.