...the world-wide electronic distribution of the peer-reviewed journal literature and completely free and unrestricted access to it by all scientists, scholars, teachers, students, and other curious minds. Removing access barriers to this literature will accelerate research, enrich education, share the learning of the rich with the poor and the poor with the rich, make this literature as useful as it can be, and lay the foundation for uniting humanity in a common intellectual conversation and quest for knowledge

Budapest Open Access Initiative

Open Access (OA) literature is digital, online, free of charge, and free of most copyright and licensing restrictions...Open Access is compatible with copyright, peer review, revenue (even profit), print, preservation, prestige, quality, career-advancement, indexing, and other features and supportive services associated with conventional scholarly literature.

Peter Suber, Director of the Harvard Open Access Project

Open access:

• can be peer-reviewed, in fact the major open-access publications and initiatives insist on it.  
• can be applied to books, journals, journal articles, videos, or any products of scholarly research.
• allows anyone to access information by removing the cost burden and other access barriers from the reader. 
• isn't free of production costs, however, and several OA business models exist.

Open Access and Scholarship

Open Access is completely compatible with peer-review and can be just as high-quality as traditionally published research.  In fact, making a work open access has been shown to increase its readership and therefore its impact. OA therefore promotes scholarship by allowing researchers access to more information, and allows access for researchers in non-traditional settings.  OA makes information available to teachers and students at all levels.

Open Access does not take away an author's rights, but often allows an author to retain more rights to his or her work.

Open Access and Publishing

Open Access is a well-established publishing model.  It has been shown to be sustainable, and even profitable.  It is important to note that OA exists only with the permission of the copyright holder, and is therefore legal.  Many of the major publishers are offering at least some Gold-model OA options, often in hybrid models where the author can pay a fee to have the article made openly available.  Currently, OA options vary greatly by publisher and journal.  A list of publishers that offer fee-based OA is maintained by the SHERPA/RoMEO group at the University of Nottingham.

In the Green model, papers can be published traditionally.  There are several possibilities, depending on the publisher's consent.  The information may be made available to a closed group, such as a campus.  There may also be a delay, often one year, before the article becomes openly available.  Alternately, the publisher may allow the pre-print to be openly available, but not the published version.  A list of publishers allowing use of their material in repositories is available from SHERPA/RoMEO