LCThe Metadata Encoding and Transmission Standard (METS) is one of the foundational XML-based standards for digital library infrastructure. It provides a container format that brings together descriptive, administrative, and structural metadata about digital objects into a single, coherent package. Widely adopted by libraries, archives, and digital preservation programs worldwide, METS has played a central role in enabling the management, exchange, and long-term stewardship of digital collections.
Background
METS emerged in the early 2000s from the Digital Library Federation (DLF), building on earlier work with the Making of America II (MOA2) project. The need was clear: digital libraries required a standard way to package the many kinds of metadata associated with complex digital objects -- bibliographic descriptions, technical details about file formats, structural information about how pages or components relate to one another, and rights and provenance data. The Library of Congress took on maintenance of the standard through its Network Development and MARC Standards Office, and a dedicated METS Editorial Board was established to guide its ongoing development.
In March 2025, the METS Editorial Board released METS 2, a simplified version of the schema designed to reduce complexity while retaining the core packaging model. METS 1 (with version 1.12.1 as the last iteration) remains available and is still in wide use.
Purpose and Scope
METS serves as a packaging or wrapping standard for digital objects. It does not define its own descriptive or administrative metadata vocabularies; instead, it provides a framework into which metadata expressed in other schemas (Dublin Core, MODS, PREMIS, MIX, and many others) can be embedded or referenced.
A METS document is organized into several major sections:
- Descriptive Metadata (dmdSec) -- bibliographic or descriptive information, typically using an external schema such as MODS or Dublin Core
- Administrative Metadata (amdSec) -- technical metadata, rights metadata, source metadata, and digital provenance, often using schemas like PREMIS or MIX
- File Section (fileSec) -- an inventory of all content files that make up the digital object
- Structural Map (structMap) -- a hierarchical outline of the digital object, linking logical structure to physical files
- Structural Links (structLink) -- hyperlinks between structural map nodes
- Behavior Section (behaviorSec) -- executable behaviors associated with the object
Serializations and Technical Formats
METS is defined as an XML Schema (XSD). All METS documents are XML instances conforming to the METS namespace (http://www.loc.gov/METS/). The schema supports extension through the use of external schemas for descriptive and administrative metadata sections.
METS 2 introduces a streamlined XSD that reduces the number of elements and attributes while maintaining the same fundamental packaging model.
Governance and Maintenance
The standard is maintained by the METS Editorial Board in collaboration with the Network Development and MARC Standards Office at the Library of Congress. The Editorial Board meets regularly, with meeting minutes published on their GitHub wiki. Community discussion takes place on a dedicated METS listserv. The Board periodically issues calls for new members, most recently in February 2026.
Development work, including the METS schema itself and associated tools, is hosted on GitHub under the mets organization.
Notable Implementations
METS is used extensively across the digital library and cultural heritage sectors:
- The Library of Congress uses METS for managing its digital collections
- The METS Implementation Registry lists institutions and systems that have adopted the standard
- Digital preservation systems such as Archivematica, Rosetta (Ex Libris), and DSpace use METS as a Submission Information Package (SIP) or Archival Information Package (AIP) format
- The BagIt-based transfer packages used by many institutions often wrap METS documents
- METS is referenced in the OAIS (Open Archival Information System) reference model implementations
Related Standards
- MODS (Metadata Object Description Schema) -- frequently embedded in METS descriptive metadata sections
- PREMIS (Preservation Metadata: Implementation Strategies) -- commonly used in METS administrative metadata sections for digital provenance
- Dublin Core -- another common descriptive metadata vocabulary used within METS
- ALTO (Analyzed Layout and Text Object) -- often used alongside METS for OCR and page layout data