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CLOCKSS is a not-for-profit digital preservation archive for scholarly journals and books, run jointly by publishers and research libraries. Its copies of publisher content are held out of public view and are released only after a defined trigger event and a decision by its Board, which is why it is usually described as a dark archive. This page explains how that pipeline works, who governs it, how to check whether a journal you care about is covered, and how CLOCKSS differs from LOCKSS and Portico. Facts below come from the CLOCKSS, LOCKSS and Portico websites, read on 2026-11-07.
What CLOCKSS is
CLOCKSS describes itself as a financially secure, independent non-profit 501(c)(3) organization whose purpose is to preserve the work and knowledge of scholars. It preserves content that publishers have licensed to it so that scholarship survives if a publisher stops hosting it. It is built on the open-source LOCKSS (“Lots Of Copies Keep Stuff Safe”) preservation technology developed at Stanford Libraries.
In the sense used in preservation work, CLOCKSS is a dark archive: publishers keep serving their own content in the normal way, and the CLOCKSS copy is not a second public access point. It becomes publicly readable only when it is triggered (see below). For the wider vocabulary, see the CASRAI entries for data repository and the OAIS Reference Model (ISO 14721), the standard framework many preservation archives describe themselves against.
Who runs it and what it covers
CLOCKSS is governed by a Board of Directors with an equal number of librarians and publishers. According to its About page, the Board decides policies, procedures and priorities, sets annual fees, and decides when to trigger content. Libraries and other institutions take part through the Digital Archive Community.
- Ingest: publishers sign an agreement giving CLOCKSS preservation rights. Content reaches CLOCKSS either by CLOCKSS harvesting the publisher’s site or through a designated SFTP site. Ingest servers sit at Rice University, Indiana University and Stanford University, where content is verified so that copies match.
- Storage: twelve CLOCKSS nodes at twelve major academic institutions hold the long-term copies. The nodes audit one another’s holdings and repair damaged copies, using LOCKSS polling and repair technology.
- Mirror sites: CLOCKSS lists mirror repository sites at 12 academic institutions worldwide.
- Scale: the CLOCKSS Keepers reports, last updated 2026-10-05 when read, count 43,176 serial titles and 533,374 book titles as preserved, in progress or committed. The counts change monthly.
What a trigger event is and what happens after it
Preserved content is released only after a trigger event and a Board decision. CLOCKSS’s How CLOCKSS Works page names technological, economic, environmental and political disruption as the kinds of threat the archive guards against, and states that all triggered publications are released under Creative Commons open access licenses. It does not publish a single-sentence definition of trigger conditions, so the clearest guide is a real case.
On 18 December 2017 CLOCKSS announced the trigger of 21 journals after Sage Publishing ceased publishing those titles, following its late-2016 purchase of the Libertas Academica portfolio. The CLOCKSS announcement states that the content would otherwise no longer be available online; the journals became openly available under a Creative Commons license and are listed on CLOCKSS’s Triggered Content page.
How to check whether a journal or book is preserved
This is the practical step the promotional pages skip. CLOCKSS publishes its preservation status as downloadable reports rather than a search box:
- Open the CLOCKSS Keepers page at reports.clockss.org/keepers.
- Choose the report you need: Serials, Books or Triggered serials. Each is offered as CSV or HTML.
- Find the publisher and title. The report shows, per publisher and title, which volumes are preserved and which are still in process.
- Note the report date. The reports update on the first day of each month at about 12:00 UT.
- For a cross-archive view, check the Keepers Registry at keepers.issn.org, in which CLOCKSS participates alongside other preservation agencies.
Library and publisher staff can use this to document preservation coverage for a licensed collection. It is evidence of status at the report date, not a guarantee that a title will be triggered or released.
Strengths and limits
Strengths
- Governance is balanced between librarians and publishers, and the trigger decision rests with that Board.
- Storage is distributed across institutions, with nodes that audit and repair each other.
- Triggered content is released openly, so a title that disappears from its publisher does not disappear from the record.
- Preservation status is publicly reported by publisher and title.
Limits
- It is not an access service. Until a trigger, the preserved copy is not offered as a public read-through; day-to-day access remains with the publisher.
- Participation is by publisher agreement, so a journal appears only if its publisher has arranged for it to be preserved.
- Trigger conditions are decided by the Board; the public pages describe the process, not an automatic rule.
CLOCKSS vs LOCKSS vs Portico
The three names are often confused. LOCKSS is the technology and program; CLOCKSS is one network built on it; Portico is a separate preservation archive.
| Service | What it is (per its own site) | Run by | Who takes part |
|---|---|---|---|
| CLOCKSS | Community-governed archive of publisher content, released after trigger events | Independent non-profit; Board of equal numbers of librarians and publishers | Publishers (by preservation agreement) and the Digital Archive Community of libraries |
| LOCKSS Program | Open-source technologies and services for distributed digital preservation; powers CLOCKSS; also supports networks such as the Global LOCKSS Network, where libraries keep local copies of e-journals and e-books | Stanford Libraries | Libraries and other memory organizations, plus partner networks |
| Portico | Community-supported preservation archive for e-journals, e-books and digital collections; content becomes accessible after trigger events | ITHAKA, a nonprofit | Libraries and publishers |
For how a publisher membership body treats preservation, see the CASRAI guide to OASPA membership criteria. For why long-term preservation commitments belong in research planning, see preservation commitment in a DMP.
FAQ
What does CLOCKSS mean?
It is the name of the preservation archive, a controlled network built on LOCKSS technology and governed jointly by publishers and libraries.
What is the difference between CLOCKSS and LOCKSS?
LOCKSS is the Stanford Libraries preservation program and software. CLOCKSS is a community-governed archive of publisher content that uses that technology; the LOCKSS Program says it powers CLOCKSS. Libraries can also use LOCKSS in networks of their own, such as the Global LOCKSS Network.
Is CLOCKSS free?
The CLOCKSS About page states that its Board sets annual fees but publishes no amounts there. Costs for a given publisher or library should be taken from CLOCKSS directly.
How do I join CLOCKSS?
Publishers join by signing an agreement that gives CLOCKSS preservation rights. The CLOCKSS site provides a Join CLOCKSS page at clockss.org/join-clockss.
Is my journal in the CLOCKSS archive?
Check the Serials report on the CLOCKSS Keepers page, as described above, and note the report date.
Sources
- CLOCKSS, About: clockss.org/about (read 2026-11-07)
- CLOCKSS, How CLOCKSS Works: clockss.org/about/how-clockss-works (read 2026-11-07)
- CLOCKSS Keepers reports: reports.clockss.org/keepers (read 2026-11-07; last updated 2026-10-05)
- CLOCKSS, trigger of twenty-one Sage Publishing journals, 18 December 2017: clockss.org announcement (read 2026-11-07)
- LOCKSS Program: lockss.org (read 2026-11-07)
- Portico: portico.org (read 2026-11-07)
