A lexical transducer, first discussed in Karttunen, Kaplan and Zaenen 1992, is a specialised finite-state automaton that maps inflected surface forms to lexical forms, and vice versa. The lexical form consists of a canonical representation of the word and a sequence of tags that show the morphological characteristics of the form in question and its syntactic category. For example, a lexical transducer for French might relate the surface form veut to the lexical form vouloir+IndPr+SG+P3. In order to map between these two forms, the transducer may contain a path like the one shown in Fig. 1.