The importance of comprehensive annotations for learning resources is widely recognized. However, it is often unclear how these annotations should be created. A promising solution might be that learners annotate learning resources during execution of learning processes. This paper examines tagging as a learner-driven approach that can be used to get annotations on a collaborative level. The characteristics of learner-generated annotations in learning scenarios and the applicability of these annotations to describe learning resources are investigated. As empirical grounding, the results of three independent experiments are presented in order to inform decisions concerning the establishment of stitutionalized settings deploying tagging approaches.