This book constitutes the refereed proceedings of the 6th International Conference on Conceptual Structures, ICCS'98, held in Montpellier, France, in August 1998. The 20 revised full papers and 10 research reports presented were carefully selected from a total of 66 submissions; also included are three invited contributions. The volume is divided in topical sections on knowledge representation and knowledge engineering, tools, conceptual graphs and other models, relationships with logics, algorithms and complexity, natural language processing, and applications.