In this chapter, we examine the history and theory underlying social tagging as annotation: first from the perspective of classification research; and second from the perspectives of knowledge representation and knowledge management. Using the context meta-model of the annotation, we demonstrate that the model is adequately represented in existing KR theory: specifically, from the perspective of socially constructed meaning in community networks. Furthermore, the set of tagging representations (triadic networks of individual, object and annotation) are well explored throughout the knowledge representation domain. In contradistinction to many commentators, we conclude that social tagging may effectively be explored via a multidisciplinary approach linking knowledge representation and classification research and creating an open domain network.