Meeting the United Nations’ Sustainable Development Goals will require additional investments of $2.5 trillion a year in things like health care and education for the world’s poorest people, according to UNCTAD, a UN agency. The term blended finance appeared referring to a strong mixture of public, private and charitable money, a way to make the limited pool of money available for worthy causes go further. The idea of using public funds to attract private money is a venerable one. For it to change development finance fundamentally it will have to become easier to scale up.