Open access (OA) comes in two forms, Gratis versus Libre: Gratis OA is free online access and Libre OA is free online access plus some additional usage rights.^[1] OA’s primary target content is articles published in scholarly journals.^[2]

Open content is similar to OA, but usually includes the right to modify the work, whereas in scholarly publishing it is usual to keep an article’s content intact and to associate it with a fixed author. Creative Commons licenses can be used to specify usage rights. OA is also similar to free content, but seldom open content, and can be extended to the learning objects and resources provided in e-learning.

OA can be provided in two ways^[3]:

• “Green OA”^[4] is provided by authors publishing in any journal and then self-archiving their postprints in their institutional repository or on some other OA website.^[5] Green OA journal publishers^[6] endorse immediate OA self-archiving by their authors.
• “Gold OA”^[7] is provided by authors publishing in an open access journal that provides immediate OA to all of its articles on the publisher’s website.^[5] (Hybrid open access journals provide Gold OA only for those individual articles for which their authors (or their author’s institution or funder) pay an OA publishing fee.)

Public access to the World Wide Web became widespread in the late 1990s and early 2000s. The low-cost distribution technology has fueled the OA movement, and prompted both the Green OA self-archiving of non-OA journal articles and the creation of Gold OA journals. Conventional non-OA journals cover publishing costs through access tolls such as subscriptions, site-licenses or pay-per-view. Some non-OA journals provide OA after an embargo period of 6–12 months or longer. See “Delayed open access journals“). Active debate over the economics and reliability of various ways of providing OA continues among researchers, academics, librarians, university administrators, funding agencies, government officials, commercial publishers, and society publishers.