The lack of affordable housing is a longstanding global challenge. Addressing this issue requires not only technical solutions but also new social practices – social innovation. This article explores the role of social innovation in increasing access to affordable housing through a theory-focused literature review. We find that the concepts often lack clarity and theoretical grounding, making it difficult to measure innovation outcomes or guide practical implementation. We adopt the social innovation ecosystem framework developed by Audretsch et al. (2022) and discuss policy, finance, culture, supports, human capital, and market perspectives. We propose an expanded version of the framework, adapted specifically for affordable housing. It introduces two key additions: explicit identification of the social innovator and the integration of spatial concepts—space and place—to capture the inherently local nature of housing initiatives. This contribution aims to advance both social innovation theory and housing research, while also informing policy and practice.