Standard techniques used in multilingual terminology management fail to describe legal terminologies as they are bound to different legal systems and terms do not share a common meaning. In the LexALP project, we use a technique defined for general lexical databases to achieve cross language interoperability between lan-guages of the Alpine Convention. In this paper we present the methodology and tools developed for the collection, de-scription and harmonisation of the legal terminology of spatial planning and sus-tainable development in the four lan-guages of the countries of the Alpine Space. 1