IntroductionThe concept of knowledge takes an important place in the representation of the legal domain, because a large part of that domain consists of rules, norms, thoughts and skills that, ideally, can be qualified as knowledge. As such, the value of knowledge is unchallenged. However, what knowledge in the legal domain amounts to, remains obscure on many occasions. This article provides a brief overview of a conceptual model (an ontology) of the legal domain, based on the concept of knowledge. The research underlying this article is a follow-up to earlier work on legal ontologies (cf. Hage 1987, Van Kralingen 1995, Visser 1995, Oskamp 1998.This article describes the potential contribution of legal theory to the analysis of the concept of knowledge in the legal domain. It does so in order to unveil the meaning of this concept, e.g., in the phrase 'legal knowledge representation'. Often, knowledge representation refers to the representation of elements of the legal domain and relations between these elements, rather than to knowledge about these entities and relations. If knowledge is considered something 'in the head' of lawyers, an analysis of the difference between knowledge about a domain and the domain itself helps to prevent conceptual confusion. Thus, it is directly relevant to a well-founded legal ontology.In this article, I explain the foundations of the knowledge-based ontology, and I explain how its constituents can be used for innovative ICT applications for use in the legal domain. First, I discuss the role and value of knowledge in a model of the legal domain, and the basic constituents of the model (section 2). Second, I demonstrate the practical relevance of the ontology by proposing a search function based on a distinction between structure and content of legal argumentation (section 3). Third, I provide a conclusion (section 4).