Social impact investing is transforming the availability of private capital for nonprofits and social enterprises, but demand is not yet meeting supply. This paper analyzes the perceived barriers faced by nonprofits in engaging with SII, arguing the need to assess differences using a policy field framework. Four parameters of a subsector are conceptualized as shaping participation in SII: the scale of investment required, embeddedness in place, the need for radical innovation, and the configuration of intermediaries. Based on 25 interviews with (...) leaders of nonprofits and intermediaries in affordable housing and community economic development in Canada, the study finds that significant barriers are a lack of knowledge of the market, inadequate financial literacy, and the challenges of measuring and valuing social impacts. In addition, nonprofits report that, in spite of the inherent importance of social impact in this form of investing, they currently make limited use of evaluation and impact metrics, and perceive that intermediaries and investors, particularly in affordable housing, still put a greater emphasis on financial over social returns. (shrink)