Self-archiving is the act of (the author's) depositing a free copy of an electronic document online in order to provide open access to it. The term usually refers to the self-archiving of peer-reviewed research journal and conference articles, as well as theses and book chapters, deposited in the author's own institutional repository or open archive for the purpose of maximizing its accessibility, usage and citation impact. The term green open access has become common in recent years, distinguishing this approach from gold open access, where the journal itself makes the articles publicly available without charge to the reader.
Self-archiving was first explicitly proposed as a universal practice by Stevan Harnad in his 1994 online posting "Subversive Proposal" (later published in Association of Research Libraries) although computer scientists had been practicing self-archiving in anonymous archives since at least the 1980s (see CiteSeer) and physicists had been doing it since the early 1990s on the web (see arXiv).
The concept of green open access was coined in 2004 to describe a “mode of publishing in non open access journal but also self archiving it in an open access archive”. Different drafts of a paper may be self-archived, such as the internal non-peer-reviewed version, or the peer-reviewed version published in a journal. Green open access through self-archiving was initially enabled through institutional or disciplinary repositories, as a growing number of universities adopted policies to encourage self-archiving. Self-archiving repositories do not peer-review articles, though they may hold copies of otherwise peer-reviewed articles. Self-archiving repositories also expect that the author who self-archives has the necessary rights to do so, as copyright may have been transferred to a publisher. Therefore it may only be possible to self-archive the preprint of the article.