This paper presents the text of remarks delivered at the 2012 Social Finance Forum held at the MaRS Discovery District on November 8-9, 2012. Social Return on Investment is an evaluation methodology that seeks to move the assessment process from a focus on cost alone to one that includes value. It gives the social field the tools and language to get important issues heard at multisectoral tables where these concerns are often misunderstood, undervalued or dismissed as unimportant. Despite its vital contribution, there are serious philosophical, conceptual and methodological challenges embedded in this approach. These include the focus on quantification, the possibility of ‘creaming’ program participants most likely to succeed, the problem of attribution and the need to take into account key developments in the broader economic and social context.