Extended definition
Plan S is an open access policy initiative launched in September 2018 by cOAlition S, an international coalition of research funders initially coordinated by Science Europe and the European Research Council Executive Agency. The central principle, synthesized in the original slogan, is direct: “With effect from 2021, all scholarly publications on the results from research funded by public or private grants provided by national, regional and international research councils and funding bodies, must be published in Open Access Journals, on Open Access Platforms, or made immediately available through Open Access Repositories without embargo.” Full implementation began in 2021. Plan S offers three compliance routes: publication in a fully open journal (gold route); deposit in an open repository with a Creative Commons license at the time of publication (green route); and publication in a hybrid journal covered by a transformative agreement — an institutional transition agreement toward open access. Default license is CC BY, with rights retention by the author.
When it applies
Plan S applies to any publication resulting from research funded by a cOAlition S signatory — Wellcome Trust, UK Research and Innovation, Horizon Europe (successor to Horizon 2020), Bill & Melinda Gates Foundation, FCT (Portugal), among others. Researchers on international collaborative projects with any co-investigator funded by a signatory must comply. Journals that fail to meet the policy’s criteria — including most hybrid journals without a transformative agreement — become ineligible for publication within Plan S funding.
When it does not apply
It does not apply to publications without funding from signatories. Non-signatory funding agencies do not directly impose Plan S — though journals are progressively aligning to global policies. Plan S does not mandate publication in high-impact-factor journals; the criterion is openness, not prestige. It does not cover books, book chapters, and monographs the same way it covers articles — Plan S for books has a distinct timeline and criteria, with more gradual adoption.
Applications by field
— Natural and biomedical sciences: the primary territory; Wellcome and UKRI are massive funding sources, and adherence is central. — Engineering and computer science: ERC and Horizon Europe cover much of European funding, requiring compliance. — Social sciences and humanities: slower adoption; open access monograph models still in transition. — International collaborative research: almost any multi-country project today has at least one co-investigator under Plan S — an effect of indirect coverage.
Common pitfalls
The first pitfall is assuming that publishing in a hybrid journal satisfies Plan S — it only satisfies if the journal is covered by a specific transformative agreement, with the list published by cOAlition S and updated periodically. The second is confusing Plan S with open access in general — Plan S is a specific mandate, with criteria more rigorous than many institutional open access policies. The third is failing to negotiate rights retention: the cOAlition S Rights Retention Strategy allows the author to deposit the accepted manuscript with a CC BY license even in journals without a gold route — but requires explicit action at submission. The fourth is misunderstanding costs: APCs (Article Processing Charges) in gold journals range from 1,000 to 10,000+ USD; institutional transformative agreements cover APCs but not at all journals. The fifth is assuming that an institutional repository satisfies the green route without proper licensing — deposit without CC BY or equivalent does not satisfy the policy.