What Is Open Access?

Open access is a publishing model for scholarly research in which the final work is made freely available to any reader without subscription fees, per-article charges, or other access barriers. The term encompasses both the act of removing financial restrictions and the broader set of practices, licenses, and infrastructure that sustain free availability over time. The Budapest Open Access Initiative, convened in 2002, provided the first widely adopted definition and distinguished open access from simple free-of-charge availability by requiring that readers also have the right to read, download, copy, and distribute the work.

Open access applies to journal articles, conference papers, book chapters, datasets, and software. The boundaries of the concept are defined in practice by licensing, repository infrastructure, and the policies of funding agencies, institutions, and publishers. Major research funders, including the National Institutes of Health and the European Research Council, now require grant recipients to make publications openly available within specified embargo windows, which has accelerated adoption across disciplines.

Open Access Publishing Models

Three publishing routes dominate current practice. Gold open access means the final published version is immediately and permanently free on the publisher's site, typically funded by article processing charges (APCs) paid by the author or their institution. Hybrid journals offer a mixed model in which a subscription journal makes individual articles open access upon payment of an APC while keeping the rest behind a paywall.

Green open access, also called self-archiving, allows authors to deposit preprints or accepted manuscripts in institutional or disciplinary repositories, independently of the publisher's own site. Embargo periods imposed by publishers govern when the deposited version may be made publicly available, and these periods vary from zero to 24 months. Diamond open access removes charges for both readers and authors: community-led journals, often funded through library consortia or research institutions, publish without APCs and without subscriptions. This model has grown in disciplines where professional societies and universities historically subsidized journals directly, as described in the overview of green, gold, and diamond open access models from the open-access.network resource.

Repositories and Preprint Servers

Repositories are the technical infrastructure that makes green open access functional. Institutional repositories, operated by universities and research organizations, collect and preserve output from affiliated researchers. Disciplinary repositories serve fields regardless of institutional affiliation: arXiv serves physics, mathematics, and computer science; PubMed Central handles biomedical literature; SSRN covers social sciences and economics.

Preprint servers, a subset of repositories, allow researchers to post manuscripts before peer review, enabling rapid dissemination of findings. arXiv, operated by Cornell University Library, hosts over two million preprints and has become the primary record of priority for many physics and computer science results. The distinction between a preprint and the peer-reviewed version-of-record has implications for citation practices and for the reliability assessments readers bring to open-access content.

Licensing and Policy

Creative Commons licenses are the standard mechanism for specifying what readers may do with open-access content. The CC BY license, requiring only attribution, is the most permissive and is favored by major funders because it permits text and data mining, translation, and reuse in derivative works without negotiating additional permissions. More restrictive licenses, such as CC BY-NC (noncommercial only) or CC BY-ND (no derivatives), are considered open access in the broad sense but limit computational reuse.

Institutional open access policies, including those mandated by governments through legislation such as the US OSTP memo of 2022, require that federally funded research be made publicly available immediately upon publication. The NIH Public Access Policy, which preceded the broader mandate, requires that NIH-funded research appear in PubMed Central within 12 months of publication and serves as the institutional template for similar policies worldwide.

Applications

Open access has applications in a range of fields, including:

• Scientific research, accelerating literature discovery and cross-disciplinary synthesis
• Public health, enabling practitioners in low-resource settings to access clinical evidence
• Education, supporting open course materials and open textbook development
• Government policy, making publicly funded research available to legislators and agencies
• Text and data mining, allowing computational analysis of large scholarly corpora