Investors in for-profit companies have clear measures of company performance in meeting their economic objectives. However, the effectiveness of investments in not-for-profit organizations is more difficult to measure, since a significant objective of these organizations is social improvement. This paper introduces the concept of “social return on investment (SROI),” in which socio-economic results are quantified together with traditional financial measures. The methodology used by the Roberts Enterprise Development Fund (REDF) is briefly outlined as an example of the implementation of SROI measurement.