Media Source Inc. (MSI) is an American company based in Plain City, Ohio. It began in 1980 as Pages and changed its name in March 1999. It owns Horn Book, including The Horn Book Magazine, Junior Library Guild, Library Hotline, Library Journal (acquired in 2010), and School Library Journal (acquired in 2010), and Digital Shift. All of these holdings are under its subsidiary MSI Information Services, the primary trade name under which the company does business. MSI was purchased by the private equity firm RLJ Equity Partners in 2011.