This paper aims to provide an introduction and overview about the social investment market for OECD member countries. Social investment is becoming increasingly important as a way to address both social and economic challenges. Several OECD member countries have been active in creating policies and support mechanisms for social investment. This paper seeks to provide background information on social investment, demonstrate how the market is evolving, and highlight the role that policymakers can play in facilitating the development of the market. This market has evolved over the past decade as the result of a number of factors, including a growing interest by individual and institutional investors in tackling social issues at the local, national or global level. The growth of social enterprises over the past several decades has also contributed to the emergence of social investment. Resultantly, new financing models are emerging at multiple levels and in parallel to traditional markets.