This article is an overview of social cataloguing trends for health librarians. Although a number of articles in the literature discuss social bookmarking or folksonomic tagging [2–5], there is a paucity of information about social cataloguing and its relevance for health libraries. Social cataloguing refers to Web-based applications that allow users to tag and track books and other items in an online inventory or personal filing system [6] (see applications in Appendix A). Social cataloguing sites (SCSs), such as LibraryThing (http://www. librarything.com/) or Shelfari (http://www.shelfari.com/), make it possible for users to catalogue and discuss books with like-minded readers from around the world. In some ways, like other popular Web 2.0 tools such as YouTube (http://www.youtube.com/), Delicious (http://delicious.com/), and SlideShare (http://www. slideshare.net), SCSs facilitate “social discovery” and community collaboration by using tags (user-determined descriptors) to describe books and audiovisual media [6]. Put simply, tags contain information that a user might need to describe or retrieve the item in question and are not limited in number or scope. These descriptors are sometimes displayed in weighted lists as “tag clouds” or concept maps. With the exception of a few oblique references to the topic, the health library literature is surprisingly silent on the issue of social cataloguing [2,4,7]. A recent general paper in Library Hi Tech, however, looked at the possibility of augmenting the Library of Congress Subject Headings (LCSH) in library catalogues with the tags found in LibraryThing [8]. The authors found instances of concepts expressed as tags in LibraryThing that were missing from the more formal LCSH catalogue description. Their conclusion was that a hybrid system combining LCSH and folksonomic tags would result in richer metadata and, ultimately, a more multifaceted “visual” library catalogue. In terms of navigation and accessibility, this approach would give users the best of both worlds. As the volume of born-digital articles in biomedicine increases, there is a need to find novel ways to generate metadata for knowledge objects (i.e., scientific articles, books, audiovisual materials, and social media). Do social cataloguing practices hold at least part of the solution to the information glut created by Web 2.0? Tools such as LibraryThing (and even some of the new features in WorldCat) exemplify how principles of the 2.0 era (i.e., user tagging, commenting, and rating systems) can be integrated into catalogues to supplement libraries’ descriptive and organizational activities [9]. SCSs may also be critical in tagging articles in blogs and wikis — today’s version of grey literature — as well as medical photos and streaming videos archived on various sites.