#Abstract
We study joint financing between profit-motivated and socially motivated (impact) investors and derive conditions under which impact investments improve social outcomes. When project owners cannot commit to social objectives, impact investors hold financial claims to counterbalance owners’ tendencies to overemphasize profits. Impact investors’ ownership stakes are higher when the value of social output is higher, and pure nonprofit status may be optimal for the highest valued social projects. We provide guidance about the design of contingent social contracts, such as social impact bonds and social impact guarantees.