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.