Open access

Open access (OA) is a set of principles and a range of practices through which nominally copyrightable publications are delivered to readers free of access charges or other barriers. With open access strictly defined (according to the 2001 definition), or libre open access, barriers to copying or reuse are also reduced or removed by applying an open license for copyright, which regulates post-publication uses of the work.

The main focus of the open access movement has been on "peer reviewed research literature", and more specifically on academic journals. This is because:

Whereas non-open access journals cover publishing costs through access tolls such as subscriptions, site licenses or pay-per-view charges, open-access journals are characterised by funding models which do not require the reader to pay to read the journal's contents, relying instead on author fees or on public funding, subsidies and sponsorships. Open access can be applied to all forms of published research output, including peer-reviewed and non peer-reviewed academic journal articles, conference papers, theses, book chapters, monographs, research reports and images.

There are different models of open access publishing and publishers may use one or more of these models.

Different open access types are currently commonly described using a colour system. The most commonly recognised names are "green", "gold", and "hybrid" open access; however, several other models and alternative terms are also used.

In the gold OA model, the publisher makes all articles and related content available for free immediately on the journal's website. In such publications, articles are licensed for sharing and reuse via Creative Commons licenses or similar.

Many gold OA publishers charge an article processing charge (APC), which is typically paid through institutional or grant funding. The majority of gold open access journals charging APCs follow an "author-pays" model, although this is not an intrinsic property of gold OA.

Self-archiving by authors is permitted under green OA. Independently from publication by a publisher, the author also posts the work to a website controlled by the author, the research institution that funded or hosted the work, or to an independent central open repository, where people can download the work without paying.