The paper “How to monitor and measure Diversity, Equity and Inclusion: the UN Global Compact Network Italy D&I Observatory’s Guidelines,” produced as part of the D&I Observatory of the UN Global Compact Network Italy, is the result of the collaboration with more than 25 Italian business and non-business entities, the International Labor Organization (ILO) Office for Italy and San Marino, the Italian Association for People Management (AIDP) and various experts in the field. The paper is aimed primarily at Business Executives, HR Managers, Sustainability experts and all those involved in promoting DE&I within their companies. It provides various practical tools for mapping the main national and international standards on the topic, guidelines and recommendations for effectively measuring business initiatives, and 15 case studies from companies of different industrial sectors and sizes. Moreover, thanks to experts’ recommendations, the paper covers several crucial aspects, such as principles and the legislative landscape, company trends, and the assessment of diversity and inclusion, as well as advice on how to overcome data collection challenges and how to measure the value and impact of DE&I initiatives, including along supply chains.