Over 80 modeling tools for mapping ecosystem services have been developed to help decision-makers better understand their local systems. These often consist of a set of models, each representing a particular ecosystem service. However, the usefulness of these modeling tools to support decision-making in practice is limited, partly because governments or other institutions lack the technical capacity and resources to run the models. A number of publications provide guidance on methods for assessing ecosystem services, including using modeling. However, these publications are generally written by technical experts for other trained professionals, rather than for decision-makers. This guide was developed for technical advisors to government officials, business people, investors, and others who need to draw on ecosystem assessments to inform decision-making. It assesses several types of ecosystem service modeling tool, discusses issues involved in modeling ecosystem services, and provides guidance on how to choose the right model to address a specific policy question. It especially targets advisors and decision-makers in developing countries who are not experts in ecosystem service modeling and who have limited information and technical resources, but must make decisions about natural resource management in relation to ecosystem services.