Open access is the practice of making peer-reviewed research literature freely available online, free of most copyright and licensing restrictions, so that anyone may read, download and reuse it. The concept was formally defined by the 2002 Budapest Open Access Initiative and reinforced by the 2003 Berlin Declaration, both of which describe free availability on the public internet alongside the right to reuse work with proper attribution.
Understanding open access means understanding two things at once: the routes by which an article becomes openly available, and the licences that govern what readers may do with it. The two are related but distinct, and policy frameworks such as Plan S operate across both.
How open access is defined
The Budapest Open Access Initiative (BOAI) defined open access as literature that is freely available to read, with users permitted to copy, distribute and reuse it for any lawful purpose, subject only to attribution. The Berlin Declaration added the requirement that a complete version be deposited in at least one suitable repository. Together these established that open access is about more than zero price; it is about removing permission barriers too. This distinction is often summarised as gratis open access (free to read) versus libre open access (free to read and reuse).
The main routes to open access
Several established routes describe how a work reaches readers. Each carries different cost and reuse implications for authors and institutions.
| Route | Where it is hosted | Who typically pays | Key characteristic |
|---|---|---|---|
| Gold | The publisher’s journal, immediately open | Author or funder, often via an APC | Final version of record is open at publication |
| Green | A repository (institutional or subject) | No author fee | A version is self-archived, sometimes after an embargo |
| Diamond | A community or scholar-led journal | Neither author nor reader | No charges to publish or to read |
| Hybrid | A subscription journal with an open option | Author or funder, via an APC | Individual articles are opened within a paywalled title |
The gold, green and diamond routes are explored in depth in our companion guide on green, gold and diamond open access routes explained. Hybrid publishing remains controversial because the same article can be paid for twice, through subscriptions and an article processing charge, an outcome critics call double dipping.
Creative Commons licences and reuse
Licensing determines what readers can lawfully do. Most open-access publishing uses Creative Commons (CC) licences, which let authors retain copyright while granting standardised permissions.
- CC BY permits any reuse, including commercial, with attribution. It is the licence most aligned with the BOAI definition of full reuse.
- CC BY-SA adds a share-alike condition, so derivatives must carry the same licence.
- CC BY-NC excludes commercial reuse.
- CC BY-ND permits redistribution but not derivatives.
The Directory of Open Access Journals (DOAJ) indexes journals that meet recognised quality and licensing standards, and is widely used to identify reputable fully open-access titles. Choosing a licence is a key decision for any author preparing a submission; our guidance for authors covers how licence choice interacts with funder mandates.
Embargoes and the green route
Under the green route, publishers may impose an embargo period during which the self-archived version cannot be made public, typically applied to subscription titles to protect their commercial model. The version permitted is often the accepted manuscript rather than the final published version of record. Repositories listed by institutions and disciplines, such as preprint servers, support this route at no cost to authors.
Plan S and cOAlition S
Plan S is a policy initiative launched by a group of research funders organised as cOAlition S. Its central principle is that research resulting from funded grants must be published in compliant open-access venues or made openly available without embargo, with funders willing to cover reasonable costs. Plan S has accelerated interest in fee-free models, and recent developments are tracked in our coverage of Plan S and diamond open access in 2026. The policy sits within the broader knowledge equity agenda, which treats open access as a route to fairer participation in scholarship.
APCs versus no-fee models
Article processing charges (APCs) fund gold and hybrid publishing by shifting costs from readers to authors or their funders. While this removes the paywall, it can create a barrier for researchers without grant support, particularly in lower-income settings. Diamond open access avoids charges entirely by funding publication through institutions, libraries or scholarly societies, and is increasingly seen as the most equitable model. The trade-off is sustainability, since diamond journals depend on continuing non-commercial support.
Frequently asked questions
Is open access the same as free to read?
Not exactly. Free to read corresponds to gratis open access. The fuller libre form, defined by the Budapest and Berlin declarations, also grants reuse rights, usually through a Creative Commons licence such as CC BY.
What is the difference between gold and diamond open access?
Both make the final version openly available at publication. Gold open access is often funded by an article processing charge, whereas diamond open access charges neither authors nor readers, relying instead on institutional or society support.
Does Plan S require a specific licence?
Plan S strongly favours licences that permit full reuse, with CC BY as the default expectation, so that funded research can be read and built upon without permission barriers.
Where can I check whether a journal is genuinely open access?
The Directory of Open Access Journals (DOAJ) is a widely used index of vetted fully open-access journals. You can also consult our standards dictionary for definitions of the key terms used across open-access policy.
