CiteULike was a web service which allowed users to save and share citations to academic papers. Based on the principle of social bookmarking, the site worked to promote and to develop the sharing of scientific references amongst researchers. In the same way that it is possible to catalog web pages (with Furl and delicious) or photographs (with Flickr), scientists could share citation information using CiteULike. Richard Cameron developed CiteULike in November 2004 and in 2006 Oversity Ltd. was established to develop and support CiteULike. In February 2019, CiteULike announced that it would be ceasing operations as of March 30, 2019. When browsing issues of research journals, small scripts stored in bookmarks (bookmarklets) allowed one to import articles from repositories like PubMed, and CiteULike supported many more. Then the system attempted to determine the article metadata (title, authors, journal name, etc.) automatically. Users could organize their libraries with freely chosen tags and this produces a folksonomy of academic interests. Basic principles Initially, one added a reference to CiteULike directly from within a web browser, without needing a separate program. For common online databases like PubMed, author names, title, and other details were imported automatically. One could manually add tags for grouping of references. The web site could be used to search public references by all users or only one's own references. References could later be exported via BibTeX or EndNote to be used on local computers. Creation of entries and definition of keywords CiteULike provided bookmarklets to quickly add references from the web pages of the most common sites. These small scripts read the citation information from the web page and imported into the CiteULike database for the currently logged in user. Sites supported for semi-automatic import included Amazon.com, arXiv.org, JSTOR, PLoS, PubMed, SpringerLink, and ScienceDirect. It was also possible although more time-consuming to add entries manually. Entries could be tagged for easier retrieval and organisation. More frequent tags were displayed in a proportionally larger font. Tags could be clicked to call up articles containing this tag. Sharing and exporting entries New entries were added as public by default, which made them accessible to everyone. Entries could be added as private and were then only available to the specific user. Users of CiteULike thus automatically shared all their public entries with other users. The tags assigned to public entries contributed to the site-wide tag network. All public references could also be