Salud Mesoamerica Initiative (SMI) is a unique results-based aid initiative that rewards countries for achieving health targets in the poorest municipalities in Mesoamerica. A partnership between private and public donors and governments, it offers lessons for philanthropists, corporate social responsibility teams, and bilateral donors about how to alter development assistance from the usual model of paying for inputs to a new one in which countries are paid for achieving results for their poorest populations. What makes this model of RBA feasible is its reliance on the staff, relationships, systems, and implementation capability of the Inter-American Development Bank and the dedicated unit that supports countries. Countries commit to achieve targets that progress from system readiness metrics to outcomes. Verification is based on externally conducted household and facility surveys. Five out of the eight countries achieved first-phase targets and received a performance payment, and all countries improved on key health system metrics.