merge: date=April 2008

Open access (OA) is free, immediate, permanent, full-text, online access, for any user, web-wide, to digital scientific and scholarly material, primarily research articles published in peer-reviewed journals. OA means that any individual user, anywhere, who has access to the Internet, may link, read, download, store, print-off, use, and data-mine the digital content of that article. An OA article usually has limited copyright and licensing restrictions.

The first major international statement on open access[http://www.soros.org/openaccess/read.shtml Budapest Open Access Initiative ] was the Budapest Open Access Initiative in February 2002. This provided a definition of open access, and has a growing list of signatories. Two further statements followed: the Bethesda Statement on Open Access Publishing in June 2003 and the Berlin Declaration on Open Access to Knowledge in the Sciences and Humanities in October 2003.

OA has since become the subject of much discussion amongst researchers, academics, librarians, university administrators, funding agencies, government officials, commercial publishers, and society publishers. Although there is substantial (though not universal) agreement on the concept of OA itself, there is considerable debate and discussion about the economics of funding peer review in open access publishing, and the reliability and economic effects of self-archiving.

There are about 20-25,000 peer-reviewed journals in all across all disciplines, countries and languages. About 10 - 15% of them are OA journals, as indexed by the Directory of Open Access Journals (gold OA). Of the more than 10,000 peer-reviewed non-OA journals indexed in the Romeo directory of publisher policies[http://romeo.eprints.org/stats.php Journal Policies - Summary Statistics So Far ] (which includes most of the journals indexed by Thomson/ISI), over 90% endorse some form of author self-archiving (green OA): 62% endorse self-archiving the author's final peer-reviewed draft or "postprint," 29% the pre-refereeing "preprint."

Authors and researchers

The main reason authors make their articles openly accessible is to maximize their research impact. A study in 2001 first reported an Open Access citation impact advantage, and a growing number of studies [http://opcit.eprints.org/oacitation-biblio.html Effect of open access on citation impact: a bibliography of studies ] have confirmed, with varying degrees of methodological rigor, that an open access article is more likely to be used and cited than one behind subscription barriers. For example, a 2006 study in PLoS Biology found that articles published as immediate open access in PNAS were three times more likely to be cited than non-open access papers, and were also cited more than PNAS articles that were only self-archived.