The United Kingdom is at the forefront of a global movement to establish a social-investment market. At the heart of social investment we find finance – and financialisation. Specifically, we find: a financial market (the social-investment market); a series of financial institutions (Big Society Capital, for example); a financial instrument (the social-impact bond); and a financial practice (social investing). Focusing on the UK, given its pioneering role, this paper first provides a brief history of social investment, tracing its development from the politics of the ‘Third Way’ to the social-impact bond. It then maps the terrain of the social-investment market, explaining the main institutions and actors, and the social-impact bond. Finally, it proposes a framework for analysing the disciplinary logics of finance, which it uses to understand the promise or threat (depending on one’s perspective) of social investment and the social-investment market.