arXiv (pronounced "archive"—the X represents the Greek letter chi ⟨χ⟩) is an open-access repository of electronic preprints and postprints (known as e-prints) approved for posting after moderation, but not peer review. It consists of scientific papers in the fields of mathematics, physics, astronomy, electrical engineering, computer science, quantitative biology, statistics, mathematical finance and economics, which can be accessed online. In many fields of mathematics and physics, almost all scientific papers are self-archived on the arXiv repository before publication in a peer-reviewed journal. Some publishers also grant permission for authors to archive the peer-reviewed postprint. Begun on August 14, 1991, arXiv.org passed the half-million-article milestone on October 3, 2008, and had hit a million by the end of 2014. As of April 2021, the submission rate is about 16,000 articles per month. History arXiv was made possible by the compact TeX file format, which allowed scientific papers to be easily transmitted over the Internet and rendered client-side. Around 1990, Joanne Cohn began emailing physics preprints to colleagues as TeX files, but the number of papers being sent soon filled mailboxes to capacity. Paul Ginsparg recognized the need for central storage, and in August 1991 he created a central repository mailbox stored at the Los Alamos National Laboratory (LANL) which could be accessed from any computer. Additional modes of access were soon added: FTP in 1991, Gopher in 1992, and the World Wide Web in 1993. The term e-print was quickly adopted to describe the articles. It began as a physics archive, called the LANL preprint archive, but soon expanded to include astronomy, mathematics, computer science, quantitative biology and, most recently, statistics. Its original domain name was xxx.lanl.gov. Due to LANL's lack of interest in the rapidly expanding technology, in 2001 Ginsparg changed institutions to Cornell University and changed the name of the repository to arXiv.org. It is now hosted principally by Cornell, with five mirrors around the world. ArXiv was an early adopter and promoter of preprints. Its success in sharing preprints was one of the precipitating factors that led to the later movement in scientific publishing known as open access. Mathematicians and scientists regularly upload their papers to arXiv.org for worldwide access and sometimes for reviews before they are published in peer-reviewed journals. Ginsparg was awarded a MacArthur Fellowship in 2002 for his establishment of arXiv. The annual budget for arXiv was approximately $826,000 for 2013 to 2017, funded jointly