Almost anyone can post a paper to arXiv (I believe in practice it requires an affiliation with a University or Insittute, or endorsement from someone who has po

Almost anyone can post a paper to arXiv (I believe in practice it requires an affiliation with a University or Insittute, or endorsement from someone who has posted to arXiv previously). In that sense, posting to arXiv is not considered "publishing" a paper, though, for all practical purposes, posting to the arXiv is a good way to make people aware of your results or ideas. Posting papers to arXiv is up to the discretion of the authors. Undoubtedly, there are papers which are peer reviewed that do not have preprints posted to the arXiv. Often people will post to arXiv as the papers are going through the peer review process. This enables the community to provide feedback in addition to the peer review process. Sometimes people do not post papers to arXiv until they have already completed the peer review process, but before the paper is actually published in a journal. And, less frequently, people will post past manuscripts to the arXiv if they think the community would benefit from having easier access to that piece of work (e.g., a chapter in a book that has gone out of print, for which the author still retains copyright). I am speaking mostly from personal experience here, based on my interactions with, and postings to the astrophysics portion of arXiv[0]. Norms may differ in other fields using arXiv. [0] http://arxiv.org/archive/astro-ph http://arxiv.org/archive/astro-ph