This book constitutes the refereed proceedings of the 21st International Conference on Conceptual Modeling, ER 2002, held in Tampere, Finland in October 2002.The 30 revised full papers presented with abstracts of various invited contributions were carefully reviewed and selected from close to 130 submissions. The papers are organized in topical sections on semantics and meta-models, principles of ontology, web environments, theory and methods, methods and tools, applications for practice, applying ontology in conceptual modeling, applying ontology in coneptual modeling, systems and data integration, quality assessment, and XML and object systems.