Open Access (OA) means free, unrestricted online access to research outputs such as journal articles and books. Because the research was funded by taxpayers, it should be open and accessible to all free of charge. The idea of ​​OA originated and spread thanks to three declarations, the Budapest Open Access Initiative, the Bethesda Statement on Open Access Publishing and the Berlin Declaration on Open Access to Knowledge in the Sciences and Humanities, also known as the BBB Declaration. These declarations created an environment for OA publishing in the early 21st century for the following decades. Their statements indicated strong philosophical foundations for promoting open-minded ideas and principles.

There are two main ways to make research results available. The first is the publication of articles or books through OA on the publisher's platform, known as the Golden road. In this model, it is assumed that readers of scientific periodicals will not pay for such access even by subscription. The most common business model is that the authors of these articles pay publishers once. These costs (often just processing royalties, APCs) are usually borne by the university or research organization to which the researcher is affiliated or by a funding agency supporting the research. In other cases, the costs associated with the publication under open access are covered by contributions or other financial models. The second path involves archiving the manuscript version in the OA repository, also referred to as the Green road. Content published through the Golden Way is available immediately after publication, while manuscripts stored through the Green Way may in many cases be made available only after the self-archival embargo period (publishers request an embargo period explaining that such a period protects the value of the magazine subscription). The terms of further sharing and reuse of OA content will depend on the license under which they were made available.

Open access in the Budapest Declaration (2002): "By open access to this literature, we mean its free availability on the public Internet, allowing any user to read, download, copy, distribute, print, search or link to the full text of these articles. , search for indexing, transmit them as data for software, or use them for any other lawful purpose without financial, legal or technical barriers other than inseparable from access to the Internet itself. The only restriction on reproduction and distribution, and the sole role for copyright in this area, should be to give authors control over the integrity of their work and the right to be duly recognized and cited ”(see http://www.budapestopenaccessinitiative.org/read).

Open access in the Berlin Declaration (2003): “Open access contributions must meet two conditions: 1. the author (s) and holder (s) of the right of such grant contribution (s) to all users free of charge, irrevocable, worldwide, right of access to , and permission to copy, use, distribute, transmit and display the work in public, and to create and distribute derivative works, in any digital medium for any responsible purpose, subject to proper acknowledgment (according to customary rules, will continue to provide a mechanism for enforcing responsible use of published works, as is currently the case), as well as the right to keep a small number of copies for their personal use. 2. The complete version of the work and all supplementary materials, including a copy of the permit as above, in an appropriate standard electronic format is stored (and thus published) in at least one online repository using appropriate technical standards (eg Open Archive definitions) that is supported. and maintained by an academic institution, scientific community, government agency, or other legally established organization that provides open access, unrestricted distribution, interoperability, and long-term archiving ”(see http://openaccess.mpg.de/67605/berlin_declaration_engl.pdf).