Sharing data across organisations and jurisdictions generates economic and social value, increasingly so as progress in artificial intelligence depends on access to high-quality, domain-specific data. Data spaces promise trusted multi-party data sharing under federated governance, yet, despite significant public investment, few have reached operational and financial viability. Drawing on the analysis of more than 200 initiatives, including case studies of successes and failures, and an OECD Expert Workshop, this report examines where data spaces provide value that alternative data-sharing mechanisms cannot. In so doing, it illustrates how data spaces best suit settings with three or more parties, limited trust in any single intermediary, collective value creation and ongoing governance needs. Governance design, interoperability and trust-enhancing mechanisms underpin this value, but many face a bootstrapping problem, which eight policy considerations help address. The report supports OECD work on data free flow with trust (DFFT) and the OECD Recommendation on Enhancing Access to and Sharing of Data.