An article is ‘open access' if you are free to read, download, copy, distribute, print or search it. The author has given a non-exclusive licence for a broad (re)use, but retains the author's rights. This makes it possible to make material accessible via the Internet or to use it as lecture material.
When making an article 'open access', it is important to know which rights the author has, and if the material has been published, which rights the author has transferred to the publisher.
Extensive research has shown that open access publications are downloaded and cited more often. An example is a study done by the University of Southampton. Several other studies are mentioned in The effect of open access and downloads ('hits') on citation impact: a bibliography of studies.
It is sometimes claimed that open access magazines do not have a high impact factor. Journals such as PLoS Biology (12.916) and CA: Cancer Journal for Clinicians (87.925) have, however, shown the exact opposite. Many open access journals are indexed in the Web of Science and other databases and do have an impact factor. You can look up their impact factor in the Journal of Citation Reports.
The accessibility to knowledge is not limited by the budget available to a library or the wealth of the country where the researcher is located. Moreover, research output based on government funded research is freely available.
Most academic research is subsidised by the government. The author pays a significant sum to the publisher to publish his/her article. The author is not allowed to distribute the article (through the Internet), or must pay extra to do so. Sometimes the author loses the copyright, and is thus forced to pay an additional fee when using his/her own material for educational purposes. The publisher charges libraries and individual users large sums to consult these publications. So research funds are used two or three times just to make research results known.
Research into the financial benefits of open access has shown that libraries can save millions by implementing an open access system.
Via the 'open access' model, libraries and researchers, together with some commercial publishers, try to develop a new model in order to regain control of their own academic articles which, owing to the high subscription rates of journals and the restrictive access conditions that publishers negotiate, are sometimes not accessible to the academic researcher or the general public.
The University of Amsterdam plays an active role in making the results of academic research done worldwide, freely accessible.