Open Access implies that research publications (like articles and books) can be accessed online, free of charge by any user, with no technical obstacles (e.g. mandatory registration or login to specific platforms). Ideally, additional rights such as the right to copy, distribute, search, link, crawl and mine should also be provided.

There are two main non-exclusive routes to Open Access publications:

  • Green Open Access (self-archiving). The published work or the final peer-reviewed manuscript that has been accepted for publication is made freely and openly accessible by the author, or a representative, in an online repository. Usually, it is not allowed to publish the final manuscript, prepared for printing by the publisher, but only preprints. Some publishers request that Open Access be granted only after an embargo period (several months to several years). Green Open Access policy of various journals may be checked at SHERPA/RoMEO or How Can I Share It?.
  • Gold Open Access (Open Access publishing). The published work is made available in Open Access mode by the publisher immediately upon publication. The most common business model for reimbursement of Open Access charges is based on one-off payments by authors (commonly called APCs – article processing charges – or BPCs – book processing charges).

There are also other modes of Open Access:

  • Platinum Open Access. It is a model of scientific publishing that does not charge either a subscription or a fee from the author. Expenses related to scientific publications are covered by other means, such as volunteer work, donations, subsidies, grants, etc.
  • Hybrid Open Access (free under an open license in a toll-access journal). Open Access content is combined with content that requires a subscription or purchase. Journals charge a subscription, or the cost of downloading articles, but allow authors to open access to their article by additional payment of processing fees. This kind of publishing can double the costs for the institution in the sense that it pays twice, first time for the subscription to the entire magazine and the second time for publishing one or more articles in the same magazine.
  • Bronze Open Access. Such manuscripts are free to read on the publisher page, but without a clearly identifiable license. Unlike Gold Open Access, Bronze articles are not published in journals considered open access in the Directory of Open Access Journals (DOAJ). Unlike Hybrid, Bronze articles carry no license information. Without an identifiable license, the articles are free to read but do not allow extended reuse rights beyond reading.

Digital repository is a system of electronic services that enables archiving, permanent storage, public presentation and dissemination of various types of scientific results. The basis of the system is a digital database of integral documents representing the results of scientific work (monographs, articles in chapters, chapters in thematic annotations, primary data, audio and video materials, etc.) and bibliographic metadata that describe them. Metadata are publicly available, and access to integral documents may be restricted by copyright or other legal restrictions. In April 2019 more than 4700 repositories available, according to the Registry of Open Access Repositories.

Most common types of repositories are:

  • Institutional repositories. Repositories that are managed by research institutions to provide a place to archive and share openly papers and other research outputs.
  • Subject based repositories. Repositories that are usually managed by research communities and most of the contents are related to a certain discipline.
  • Harvesters. Repositories that are aggregate content from different repositories. It is possible to perform general searches and build other value-added services.