Medium-sized research infrastructures (up to 10 M€ initial cost or 1-5 M€ annual cost) have a considerable, yet currently largely untapped potential to enhance scientific excellence and promote collaboration in modern research. The European Strategy Forum on Research Infrastructures (ESFRI) focuses on the role of large- scale research infrastructures, whereas little attention has been paid to the role of medium-sized research infrastructures (RIs) in Europe and how facility sharing, (transnational) access, international coordination and sustainability can be stimulated. 

Access to medium-sized RI facilities is not always well-organised, and we propose measures to remedy this situation. This would contribute to the European Open Science agenda. LERU recommends that:

• Funding mechanisms are developed to make RIs sustainable. A smart strategy is needed for the RIs to remain competitive in their respective fields, and for them to be leading and agile regarding further technological developments.

• Mechanisms should be developed to encourage cooperation in investing in new RIs, especially cross-border, thereby helping to avoid unnecessary duplication.

• Supporting actions to create a more robust and better connected European network of RIs need to be continued and extended within the context of the European Open Science Cloud (EOSC).

• The academic community plays the leading role in planning and operating the RIs.

LERU proposes a set of ‘golden principles’ for RIs, describing the fundamental rules of their operations, with transparency in information and policies, solid embedding in existing organisations, and clear indicators for operational and scientific excellence, as its main aspects. We suggest that a standard checklist is developed to assess if an RI adheres to these golden principles. The checklist can be used whenever direct funding (base funding from local institutions, from national or international roadmaps) or indirect funding (new ways to involve RIs as part of a research project of the user community) is requested.

We hope that this document will help catalyse the long-term sustainability of medium-sized RIs by acting as a guide for institutions and universities on how to open the RIs and collaborate, showing how member states and EC funders can collaborate to jointly fund and open RIs, and finally as a stimulus to the EC to develop a policy to ensure the long-term sustainability of RIs.