The two models for Open Access are known as "Gold" and "Green" Open Access. These two models differ in how content is accessed, as well as in how they are funded.
Gold Open Access is when access is provided through a publisher, in much the same way as traditional scholarly journals. There are many types of Gold Open Access, depending on how the publication is funded. There are varieties where the author pays a fee the publisher to have their article published. There are also vareties that are funded through institutional subsidies (some academic institutions publish OA journals on this model) or through advertising. Some traditional scholarly journals are now offering authors a choice as to whether their article will be open or closed; these hybrid journals often follow the author-pays funding model. Gold Open Access materials typically go through the same peer review process as traditional scholarly publications. One of the most well known providers of Gold Open Access content is the Public Library of Science.
In contrast to Gold Open Access, Green Open Access is provided through repositories. Institutional repositories are collections of digital materials that can include the scholarly, creative, and administrative output of a particular institution's students, faculty, and staff. Disciplinary repositories are organized around a particular discipline rather than an institution. Unlike materials that accessed through a publisher, only a subset of the materials in a digital repository will have undergone peer review. Repositories can also contain non-peer-reviewed content, such as pre-prints, lesson plans, and data sets. One of the oldest and best-known disciplinary repositories is arXiv (pronounced 'archive'), which collects materials from Physics, Mathematics, Computer Science, Quantitative Biology, Quantitative Finance and Statistics.
Open Access Journals for Undergraduate Research