Persistent Identifiers as IRO Infrastructure was a Towards a National Collection Foundation Project. The project aimed to increase the uptake and use of PIDs for heritage collections so that they can serve as a foundational infrastructure for drawing together the national collection, delivering innovation by adopting a cross-disciplinary and cross-collections approach to the use of an existing technology. Abstract Heritage organisations in the UK house at least 200 million physical and digital objects[1]. Being able to uniquely identify these objects supports their discovery, use and curation - you cannot provide persistent or even consistent access to an item if you don't know what it is. Accession numbers are a key component in all collection and library management systems but these only cover selected objects within an individual collection. To fully realise the potential of our national collections, we need to link together collections across institutional boundaries. Persistent Identifiers (PIDs) provide a long-lasting, click-able link to a digital object, recognised by UKRI as a tool for making content Findable, Accessible, Interoperable and Reusable (FAIR)[2] and enabling citation and metrics. Supporting wider use of PIDs for collection objects, environments, specimens and related items will allow long-term, unambiguous linking that will create a digital national collection. However, the challenges, utility and wider benefits of PIDs are not well understood across the heritage sector. The project brought together best practices in the use of PIDs, building on existing work and projects. Through a mixture of workshops, surveys, desk research and case studies, the project gathered evidence to develop an effective toolkit for the sector to make wider use of PIDs and provided recommendations on an approach to PIDs for colleagues and institutions across UK heritage. [1] Keene, S; Stevenson, A; Monti, F; (2008) Collections for people: museums' stored collections as a public resource. UCL Institute of Archaeology: London https://discovery.ucl.ac.uk/id/eprint/13886 [2] Wilkinson, M., Dumontier, M., Aalbersberg, I. et al. The FAIR Guiding Principles for scientific data management and stewardship. Sci Data 3, 160018 (2016). https://doi.org/10.1038/sdata.2016.18