9 Association of Research Libraries Research Library Issues 302 — 2021 organizations need the support of the research community. The research community is also best served by open licensing of metadata that enables interoperability across systems. Libraries, IT professionals, and research offices that develop or purchase research support systems can help accelerate the adoption of PIDs by requiring that these systems be designed to integrate with identifier registries, and by advocating for open metadata and open code.4 When relying on PIDs to track and connect research, we need to be aware of the opportunities and limitations of the PIDs and the underlying research infrastructure that we use to do this. A proprietary identifier in a closed system is only useful to that system and its user base. This is a sustainability concern. PIDs developed as open infrastructure and for use in open infrastructure afford the greatest potential to implement efficient, cost-effective, long-lasting scholarly communication practices. An investment in open PID infrastructure is a strategy for making research—and insights about research—more accessible to all, and serves as a sort of insurance policy against the unpredictable events that can arise in a commercialized scholarly communication landscape. Frameworks like POSI can help distinguish which organizations or tools follow open principles and surface information about governance and sustainability. These considerations are significant factors if we are to prioritize investments in open infrastructure. Below, we explore three critical areas for investment in sustainable, open PID infrastructure: (1) library publishing and institutional repositories, (2) data services, and (3) research data management. We focus on use cases featuring digital object identifiers (DOIs), for two reasons. First, we expect that many institutional stakeholders will be familiar at least in principle with DOIs, as they are commonly visible in publications, reference lists, and databases. Second, DOIs exemplify how PIDs can be enriched with metadata and how PIDs can work in concert with each other to make research more discoverable.