In this paper we present an OWL ontology of fundamental legal concepts developed within the ESTRELLA European project. The ontology includes the basic normative components of legal knowledge: deontic modalities, obligative rights, permissive rights, liberty rights, liability rights, different kinds of legal powers, potestative rights (rights to produce legal results) and sources of law. Besides the taxonomy the ontology comprises also the semantic relations between the concepts. We hope that it may be useful for semantic access to digital legal information and for the representation of legal knowledge.