The aim of the IKAROS (Esprit project 954) is to evaluate the interest of Artificial Intelligence techniques in speech understanding. This is achieved by designing and implementing a system whose features include continuous speech, multispeaker, vocabulary of up to one thousand words, natural-type spoken language, multilingualism and railway timetable enquiry as application. A set of knowledge sources (KSs) for various levels (acoustic-phonetic, phonological, syntactic semantic and pragmatic) and an architecture that permits the closest co-operation between these KSs have been developed.