In this paper we elaborate on the subject of Computational Lexicography. We present and define the various types of dictionaries -- traditionally or electronically constructed -- and their relations. This presentation is followed by a discussion of the role of the computer in dictionary building, focussing on three stages of this process : a)data compilation, b)information organization, c) modes of use. Emphasis is given to two of the most important properties that characterize Computational Lexica, namely "reusability" and "multifunctionality". For reasons of exemplification, after a short description of the lexica used by the Eurotra Machine Translation System, we present specific cases where the above lexica can be reused, either for linguistic research or for other applications.