This guide aims to support proponents to develop a rigorous measurement framework for, and demonstrate the value of, their social impact investment proposal. It has been prepared specifically for social impact investments with the New South Wales (NSW) government only. It is not intended to specify or guide measurement in other impact investments that do not involve the NSW government and may not require the same approach. This guide provides technical advice on designing an outcomes measurement framework, and on making the economic and financial case for an intervention financed by social impact investment. Moreover, this technical guide outlines how to articulate what an intervention is trying to achieve, how the intervention is going to achieve it, and how to measure the extent to which the intervention achieves its aims. It is based on established frameworks and a large body of tested and accepted methods, which have been tailored specifically for use in this context.