Persistent identifiers (PID) for scholarly resources have been around now for more than 20 years. Since the initial launch of the Handle.net we have seen a proliferation of PID into many use cases. Some PID systems have become established parts of the science information infrastructure, in other areas we are seeing work in progress, and new use cases being proposed. In addition to the PID use cases a number of critical questions arise. These include:

- What progress has been made - what works and what lessons have we learned?
- Are there key gaps in the ways that research outputs are structured, accredited and exposed?
- How are issues of interoperability between different PID systems to be handled, and what are the implications of doing so?

As areas of discussion this session we propose:

- Use cases for PID in earth sciences (e.g. dynamic data, fine-grained access)
New use cases (e.g. provenance, reference, credit, metrics, quality, standards)
- Communities of practice and governance around PID systems
- New forms of scholarly output and communication, linked data

This is a joint session of PID operators, data systems, memory institutions, publishers and other stakeholders.