Human behavior is a key driver of all major threats to biodiversity. As such, to conserve biodiversity we must be able to influence human behavior. To this end, a number of conservation outreach efforts, including environmental education and social marketing, have been undertaken. However, these efforts have historically suffered from a lack of evaluation, leading some to question their real impact in terms of mitigating threats to biodiversity. This burden of proof has become even more severe as budgets available for conserving natural habitats and species have been stretched ever more thinly. This has forced conservation biologists to make difficult choices about where to invest their scarce resources. As such, it is crucial that conservation efforts are as efficient as possible. One approach used by businesses to improve their efficiency is the Financial Return on Investment (ROI) framework, where costs (e.g. money, time) are compared to the benefits (e.g. number of individuals, area protected) of a given conservation project and transformed into a ratio of benefit per unit of cost. This type of framework has also been used by health practitioners to account for a wider array of social and human benefits, creating the Social Return on Investment (SROI) framework. The aim of this research is to construct a SROI framework that fits the specific needs of conservation outreach projects, which deal with the key driver of all major environmental threats: human behavior. The use of SROI in conservation can help not only understand what makes some projects more efficient than others, but also inform the design and implementation of future projects through lessons learned. By providing an in-depth evaluation of conservation outreach projects, beyond simplistic “success” or “failure” labels, the use of SROI will decisively improve resource allocation and ensure that even in a climate of financial uncertainty, conservation projects deliver the most benefits possible.