DOI or a Digital Object Identifier is a persistent reference to uniquely identify a digital object. DOIs are standardised by the International Organization for Standardization (ISO) and governed by the DOI Foundation. Crossref operates one of the authorised registries for DOIs, specifically for scholarly content (whether those are book chapters, journal articles, preprints, grants or other outputs).
DOIs are actionable, meaning that usually the record of the specific object can be accessed online with the DOI link. This however depends on the availability of the source material or the archive.
While persistent identifiers (or PIDs) in general, and the DOIs in particular, allow for identification of the scholarly objects, it’s the metadata that connects the works with one another and helps human and machine users to discover them.
You might be familiar with other types of persistent identifiers, such as ORCID IDs for individual researchers and ROR IDs for scholarly institutions. You can learn more about connections between persistent identifiers in scholarly communications from the interactive chart created by MoreBrains.
These are great resources! I also did an interview with Crossref Member Experience Manager Anna Tolwinska for the Scholastica blog on how scholarly journals can become Crossref members/start registering DOIs for articles and the benefits titled, “Getting Started with DOIs at Your Journals: Interview with Anna Tolwinska, Crossref,” which may be of interest.