This paper, by Ginevra Peruginelli, examines the general issue of mapping concepts of different legal orders, with a focus on legal terminology and semantics of the law. Interoperability between legal thesauri is a possible operative solution in so far as it meets two important functions: cross-collection retrieval and cross-language retrieval. At a practical level a feasibility study, carried out by the Institute of Legal Information Theory and Techniques of the National Research Council of Italy is described. The study aims at aligning a number of thesauri used in e-government services within the EU, while testing new methods of automatic mapping.