"Open Access (OA) literature is digital, online, free of charge, and free of most copyright and licensing restrictions" (Suber). OA scholarly literature also offers these less restrictive regulations, so that they can be more accessible to students, authors, scholars, and general users.
Many OA journals adhere to the traditional peer-review process and maintain high scholarly publishing standards.
Peter Suber's overview of open access offers a more thorough introduction.
