Excitement is growing about results-based financing (RBF) for health, a financing mechanism that turns the traditional donor approach of paying for inputs on its head. RBF for health is a cash payment or non-monetary transfer made to a national or sub-national government, provider, payer, or consumer of health services after predefined results have been attained and verified. Payment is conditional on measureable actions being taken. Where RBF has been tried, experience suggests it can improve health outcomes and strengthen health systems. But there is little rigorous evidence on its impact and many questions remain: Does focusing on some health interventions lead to the neglect of others? Will the approach encourage people to cheat to receive the incentive? Is it cost-effective? Will it diminish workers’ intrinsic motivation? What about unintended consequences?