Del.icio.us is a social bookmarking tool that allows users to store, tag, and share bookmarks online. The document discusses how to get started with del.icio.us, including adding tags and browsing bookmarks. It provides examples of how some libraries use del.icio.us for research assistance, subject guides, and sharing links with patrons. The document suggests ways the library could utilize del.icio.us reference tools and bookmarks.