EOSC-ENTRUST’s vision is a network of interoperable trusted research environments (TREs) capable of supporting large-scale European research and analysis efforts on sensitive and restricted data. In this first of three briefs, we outline the importance of European investment in TRE services and offer five recommendations for funders, policymakers and national research infrastructure planners: Invest in TRE infrastructure, including hardware, software and people. Promote TRE interoperability, to create the necessary ecosystem for data linkage. Build on international standards and best practices, rather than start from scratch. Nurture TRE communities, developing the human capital and cooperation required. Build and maintain effective public engagement, maintaining our social licence for research with public data.