Abstract: Conservation investments are increasingly evaluated on the basis of their return on investment (ROI). Conservation ROI analysis quantitatively measures the costs, benefits, and risks of investments so conservancies can rank or prioritize them. This paper surveys the existing conservation ROI and related literatures. We organize our synthesis around the way studies treat recurring, core elements of ROI, as a guide for practitioners and consumers of future ROI analyses. ROI analyses involve quantification of a consistent set of elements, including the definition and measurement of the conservation objective as well as identification of the relevant baselines, the type of conservation investments evaluated, and investment costs. We document the state of the art, note some open questions, and provide suggestions for future improvements in data and methods. We also describe ways ROI analysis can be extended to a broader suite of conservation outcomes than biodiversity conservation, which is the typical focus.