Cornell University Libraries recently announced that arXiv, the free online repository for articles in physics, math, computer science, quantitative biology and statistics, now contains over half a million articles. arXiv was developed in 1991 and is the oldest online article repository in existence. Researchers upload their own articles to arXiv, and they are usually made available to the public the next day. A team of 113 volunteer moderators from around the world screen submissions and recommend whether they should be included in the repository. arXiv has long stood at the forefront of the open-access movement and served as the model for many other initiatives, including the National Institute of Health's PubMedCentral. It is currently ranked the No. 1 repository in the world by the Webometrics Ranking of World Universities. More information is available in the Press Release issued by Cornell University.