this paper, as well as utilizing such new and promising resources as on-line dictionaries. Recent work on machine-readable dictionaries offers new and interesting possibilities both for the computerassisted lexicology (see Walker 1984) and for construct- ing lexical databases derived from the definitions in machine-readable dictionaries and utilized in NLP along with other fields (see Amsler 1982, 1984a; Walker, Amsler 1986, Calzolari 1984a,b). The premises and goals of these efforts are fully compatible with our belief, first, that no AI system is ready to make the kind of decisions that lexicon building requires and, second, that 'simply having an online version of an encyclopedia [or a dictionary] would be of little use, as there is practically nothing that current AI could draw from the raw text. Rather, we must carefully re-represent the encyclopedia's knowledge -- by hand -- into some more structured form' (Lenat et al. 1986:75). Such re-representation would be necessary for Amsler's (1984a:458) 'lexical knowledge base [which] is a repos- itory of computational information about concepts' and which contains information derived from machine-read- able dictionaries, the full text of reference books, the results of statistical analysis of text usages, and data manually obtained from human world knowledge.' This paper deals primarily with the last item on Amsler's agenda. It is based on the following approach to the problem of lexicon building. The work is done by humans assisted by an interactive aid which enhances productivity and ensures uniformity. It is important to recognize that lexicon building in NLP involves the acquisition of not one entity but rather of three interre- lated but distinct lexicons, namely a) the world concept lexicon which structures our kno...