Abstract: This case study examines the use of Diigo, a social bookmarking tool, in an online class. The purpose of using Diigo in this class was to create a collaborative knowledge base on the course topic around which students might interact. Students contributed relevant links to the Diigo group, although tagging appeared somewhat haphazard. Toward the end of the course, a tagging scheme started to emerge. The brief course duration likely limited the benefits of Diigo to this group, at least where tagging was concerned. Not all students contributed in the same way; some contributed more links whereas others were heavy commenters. Link contributors did not dominate the comment-based interactions. Instead, comments were based on mutual interests, with students letting each other know when and how their contributions were valued.