There are lots of standards used in scholarly publishing that help to facilitate accessibility, data interchange, etc. They also help to reduce the operational overhead for publishers, who don’t need to reinvent the wheel.
This thread is a place to share links to applicable standards beyond metadata standards like the DOI.
As a starter for ten:
COUNTER is the industry standard for usage metrics, offering consistent and comparable usage statistics across publishers of all types. Details at https://www.projectcounter.org/
JATS (Journal Article Tag Suite) is the industry standard for journal article markup. JATS is a set of XML elements and attributes that combine to offer a comprehensive mechanism for both layout and long-term preservation. Details at https://jats.nlm.nih.gov/
KBART (Knowledge Bases and Related Tools) is a NISO standard that facilitates the transfer of holdings metadata from content providers to knowledge base suppliers and libraries. Details at https://www.niso.org/standards-committees/kbart
MARC is a standard for communicating book metadata. Details at https://www.loc.gov/marc/
OAI-PMH (Open Archives Initiative Protocol for Metadata Harvesting) offers repository interoperability. Data Providers expose structured metadata using the Protocol, which can then be harvested by Service Providers. Details at https://www.openarchives.org/pmh/
ONIX is the international standard for representing and communicating book industry product information. Details at https://www.editeur.org/
Shibboleth is an identity management system, frequently used to facilitate off-campus access to subscription tools and content. Details at https://www.shibboleth.net/
WAI / WCAG offers the Web Content Accessibility Guidelines. Details at https://www.w3.org/WAI/standards-guidelines/wcag/