A grand variety of ontologies have been developed and tested in e-learning projects recently. One of the main purposes of the most projects is knowledge reuse, but only few ontologies are used or reused in practical e-learning systems. In this monograph, we comprehensively survey the usage of ontologies in e-learning, analyze the role, current state and outline the future of ontologies related to E-Learning. We discuss how ontologies should be used in practical e-learning systems to achieve improvement of the e-learning process at the acceptable cost. We also analyze specifics of the ontologies, used in e-learning and classify them according to valuable for e-learning criteria. As e-learning domain augments knowledge, that origins are in various scientific domains, as well as social, pedagogical, and psychological ones, we present a new approach to model and manage this multiple domain knowledge by usage of the system of mapped ontologies. We also propose an architecture of the ontology library for storing mapped ontologies, useful in e-learning, that can effectively support its evolution and reuse in correspondence with rapidly changing demands in e-learning domain.