JSTOR (short for Journal Storage) is an online system for archiving academic journals, founded in 1995. It provides its member institutions full-text searches of digitized back issues of several hundred well-known journals, dating back to 1665 in the case of the Philosophical Transactions of the Royal Society. Membership in JSTOR is held by 7,000 institutions in 159 countries.

JSTOR was originally funded by the Andrew W. Mellon Foundation, but is now an independent, self-sustaining not-for-profit organization with offices in New York City and Ann Arbor, Michigan. In January 2009 JSTOR merged with ITHAKA becoming part of that organization. The latter is a non-profit organization founded in 2003 "dedicated to helping the academic community take full advantage of rapidly advancing information and networking technologies."

JSTOR was originally conceived as a solution to one of the problems faced by libraries, especially research and university libraries, due to the increasing number of academic journals in existence. The founder, William G. Bowen, was the president of Princeton University from 1972 to 1988. Most libraries found it prohibitively expensive in terms of cost and space to maintain a comprehensive collection of journals. By digitizing many journal titles, JSTOR allowed libraries to outsource the storage of these journals with the confidence that they would remain available for the long term. Online access and full-text search ability improved access dramatically. JSTOR originally encompassed ten economics and history journals and was initiated in 1995 at seven different library sites. As of November 2010^[update], there were 6,425 participating libraries. JSTOR access was improved based on feedback from these sites and it became a fully searchable index accessible from any ordinary Web browser. Special software was put in place to make pictures and graphs clear and readable.