How CLOCKSS Works: Ensuring Long-term Access to Digital Content

The CLOCKSS initiative is a partnership of libraries and publishers committed to ensuring long-term access to scholarly work in digital format. As more and more content moves online, there is growing concern that this digital content may not always be available. CLOCKSS addresses this problem by creating a secure, multi-sited archive of web-published content that can be tapped into as necessary to provide ongoing access to researchers worldwide for free.

There are many ways digital content may become unavailable, including when a publisher chooses to retire a journal. SAGE Publications, a CLOCKSS partner, recently announced that it would discontinue online access to its journal, Graft: Organ and Cell Transplantation. This represents an opportunity to demonstrate how CLOCKSS responds to a “trigger event.”

CLOCKSS publishers feed digital content, including the journal Graft, into a distributed archive housed at twelve sites around the globe. When content ceases to be available, for whatever reason, and for an agreed lapse of time, a “trigger event” is judged by the CLOCKSS Board to have occurred. Content stored in the archive is released to designated delivery platforms or hosts, ensuring unrestricted access to research literature that might otherwise have been lost.

The current CLOCKSS Board, includes executives from the world’s leading publishers — responsible for about 60% of journal content currently online — and representatives from ten leading libraries, OCLC and NII. Together they have developed a network of geographically-diverse CLOCKSS archive sites. The sites maintain “CLOCKSS boxes,” computers with storage to hold and preserve multiple copies of content from the participating publishers. These geographically-dispersed copies are under different administrative control and are continually and automatically audited against one another. These copies remain “dark,” hidden and unavailable for use, until a trigger event leads the CLOCKSS Board to “light up” the content and restore access to it.

CLOCKSS is actively recruiting additional publishers and libraries to join the initiative. For information on joining CLOCKSS, please contact

In June 2007 CLOCKSS was the inaugural winner of the Association for Library Collections & Technical Services (ALCTS) Outstanding Collaboration Citation, which recognizes and encourages collaborative problem-solving efforts in the areas of acquisition, access, management, preservation or archiving of library materials. The ALCTS is a division of the American Library Association.

In 2014, the Center for Research Libraries (CRL) announced the completion of an eight-month audit of the CLOCKSS Archive and certified the CLOCKSS Archive as a trustworthy digital repository. CLOCKSS is the only organization to earn a perfect score of 5 in the Technologies, Technical Infrastructure, and Security category. CLOCKSS also attained the highest score received by any organization that has undergone this independent audit.

The CLOCKSS initiative is funded by participating publishers and library organizations.

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