The Open Access movement has proven success in making scientific research more visible and accessible. Open Access (OA) articles receive between 3 and 6 times more citations than articles published in non-OA journals .
The tradition within scientific communities is one of sharing research results, by peer-review processes and advancing the state-of-the-art by building upon the shoulders of peers by publication and citation. Although through the internet scientific knowledge has become accessible to a growing number of people, still not the full potential of the internet has been exploited in enabling the process of discovery, usage and furthering of scientific knowledge.
Publishers of research journals, even if published online, tend to restrict access to a select group of research institutes that can afford the subscription fees. Since the 1990's more and more authors have started publishing their articles (and data) online, in freely accessible websites and repositories. This is called self-archiving .
Three initiatives in particular have helped grow Open Access - 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,  - and are recognised as historical, defining moments in the growth of this movement. There are several definitions of Open Access, see for an extensive overview Peter Suber . However, the main requirements for a contribution to be Open Access are: 1) it removes all price barriers for the users to access it (given the user has an internet connection) and 2) it removes enough permission barriers to support all the uses customary in legitimate scholarship. The only constraints an author can pose should be to give authors control over the integrity of their work and the right to be properly acknowledged and cited. These requirements can be defined more precisely as follows.
Open Access contributions are those works that satisfy two conditions:
1. The author(s) and right holder(s) of such contributions grant(s) to all users a free, irrevocable, worldwide, right of access to, and a license to copy, use, distribute, transmit and display the work publicly and to make and distribute derivative works, in any digital medium for any responsible purpose, subject to proper attribution of authorship (community standards will continue to provide the mechanism for enforcement of proper attribution and responsible use of the published work, as they do now), whether in print or online.
2. A complete version of the work and all supplemental materials, including a copy of the permission as stated above, in an appropriate standard electronic format is deposited (and thus published) in at least one online repository using suitable technical standards (such as the Open Archive definitions, ) that is supported and maintained by an academic institution, scholarly society, government agency, or other well-established organization that seeks to enable open access, unrestricted distribution, interoperability, and long-term archiving.
Establishing Open Access as a worthwhile procedure ideally requires the active commitment of each and every individual producer of scientific knowledge and holder of cultural heritage. Open Access contributions include original scientific research results, raw data and metadata, source materials, digital representations of pictorial and graphical materials and scholarly multimedia material.
As stated in the Budapest Initiative, Open Access to peer-reviewed journal literature is the goal. Self-archiving (e.g. see the arXiv.org, ) and a new generation of Open Access journals (see , ) are the ways to attain this goal. Many universities around the world have implemented scholarly repositories where their research staff can self-archive their research contributions. MIT was one of the first to develop a Free Software repository called DSpace. (MIT's DSpace Experience. A Casestudy, ).
Research shows that although 49% of research faculties has self-archived at least one article in some way, still a large part doesn't (Swan and Brown, ). Surprisingly ninety-two percent of journals has already given authors permission to self-archive, but authors self-archive only 15% of their contributions.
For increasing the author's visibility and citation index, several studies show the advantages of Open Access publishing. As Harnad and Brody show (Harnad and Brody, ), articles published in Open Access Journals have a 3 to 6 times higher citation ratio. In other words, those articles that have been published by self-archiving in Open Access journals receive 3 to 6 times more citations than the articles published in non-Open Access journals.
See an extensive overview of visibility/impact studies by Hitchcock,  on the Open Citation Project.
 Harnad, Brody, 2004, http://www.dlib.org/dlib/june04/harnad/06harnad.html
 See the ePrints Self-archiving Frequently Asked Questions, http://www.eprints.org/openaccess/self-faq/
 Budapest Open Access Initiative, 2002, http://www.soros.org/openaccess/read.shtml
 Bethesda Statement on Open Access Publishing, 2003, http://www.earlham.edu/~peters/fos/bethesda.htm
 Berlin Declaration on Open Access to Knowledge in the Sciences and Humanities, 2003, http://oa.mpg.de/openaccess-berlin/berlindeclaration.html
 Peter Suber, Open Access Overview, http://www.earlham.edu/~peters/fos/overview.htm
 Open Standards for Web Contents Interoperability: http://www.openarchives.org/
 The Open Access arXiv provides access to 529,561 e-prints in Physics, Mathematics, Computer Science, Quantitative Biology, Quantitative Finance and Statistics (date: 26/03/09): http://arxiv.org/
 Directory of Open Access Journals: http://www.doaj.org/
 A few important OA Journals: Public Library of Science , PubMed , BioMed Central ,
 A casestudy on MIT's DSpace Free Software repository http://www.dspace.org/implement/case-study.pdf
 Swan and Brown, 2005, http://eprints.ecs.soton.ac.uk/10999/
 Hitchcock, http://opcit.eprints.org/oacitation-biblio.html