In the information society of the next millenium, information retrieval over the Internet will be indispensable for everyday life, and spoken language will be an essential medium for human-machine dialogue. This paper presents an overview of an intelligent system for information retrieval based on spoken dialogue, use of key concepts, processing of unknown words, knowledge acquisition, and agent technology. Three agents are introduced to be respectively responsible for user interface, information retrieval, and information acquisition. Dialogue management through user and system modeling, implementation of information retrieval through key concepts, and inference on concepts of unknown words based on syntactic and semantic analyses of their structures, are then brie y described as the innovative features of the system.