This volume constitutes the proceedings of the Fourth International Conference on Flexible Query Answering Systems, FQAS'2000, held in Warsaw, Poland on October 25 - 28, 2000. The FQAS conference has been the premier conference focusing on one of key issues that the information society faces, namely that of providing easy, flexible, intuitive access to information for everybody. In targeting this issue, the conference draws on several research areas, such as databases, querying, information retrieval, knowledge representation, soft computing, cyberspace, multimedia systems, human-computer interaction, etc. FQAS'2000 has been preceded by the extremely successful FQAS'94, FQAS'96 and FQAS'98 conferences all held in Roskilde, Denmark. The present conference provides a unique opportunity for researchers, developers and practitioners to explore new ideas and approaches in a multidisciplinary forum. As a metaphor for flexible query answering we may consider a human intermediary who has expertise in the topic of the query, and is experienced in identifying the user's information needs and answering the needs from the available information resources. The use of knowledge on relevant contexts, available information resources, etc. , enables the expert to respond rather precisely to the needs, though the query, per se, may be imprecise, incomplete, etc. Thus, a key issue for flexible query answering system is to obtain, maintain, represent, and utilize such knowledge. This comprises domain knowledge and metaknowledge, its representation and organization in ontologies, terminologies, etc.