Abstract. Web-based tagging systems for educational resources allow users
to associate free keywords with resources to facilitate their retrieval and
reuse. This paper looks at the similarities and differences among three
different systems. We first focus on the purpose of tagging and the
incentives for users to tag educational resources. Then, we compare the
most used tags in each system. We find that even if the tagging system
design decisions differ, there is a number of similarities in tags that are
shared among more than one of the services. Moreover, our goal is to
discuss the reuse of tags across these systems and use them as a
navigational aid for a user to cross system boundaries.