This OECD Guide takes stock of the current advice, guidelines, and good practices for assessing the impact of global events. Global events (including culture, sports and business events) can have a significant impact on local development. Yet measuring this impact in a consistent, reliable and comprehensive way can be challenging. This Guide provides an overview of approaches to impact assessment, discusses the issues, challenges and considerations to be made in conducting impact evaluations, and offers a set of actions which event hosts can take to improve impact assessments. In doing so, the Guide supports the OECD Recommendation on Global Events and Local Development, which helps countries and future hosts bring greater local benefits and legacies from global events. This Guide can be read alongside "Impact indicators for culture, sports and business events: A guide, Part II".