The purpose of this study is to explore how and to what end blended finance mobilizes private investment towards the SDGs, moving away from an emphasis on private capital leverage as an efficiency metric, and relying instead on the concept of net social returns that incorporate the wider economic effects of blended finance and its cost to the taxpayer.

In the first section, we start by addressing two preliminary questions, (i) what is the end goal for blended finance practitioners, and (ii) what can we infer from economics theory as to the justification and efficiency of blended finance?

Through these lenses, we will assess in the second section some practical blended finance investment strategies: (i) creating knowledge spillovers that can affect markets’ behaviors, (ii) fixing weak links in complementary production networks.

These are not the only justifications for concessional blended finance, but they exemplify the approach based on starting with an idea about where large social returns on investment are likely to be found, and then allocating blended finance when needed to enable investments that have those characteristics.