This book constitutes the refereed proceedings of the 23rd International Conference on Conceptual Modeling, ER 2004, held in Shanghai, China, in November 2004.The 57 revised full papers presented together with three invited contributions and 8 demonstration and poster papers were carefully reviewed and selected from 295 submissions. The papers are organized in topical sections on conceptual modeling, datawarehouses, schema integration, data classification and mining, web-based information systems, query processing, web services, schema evolution, conceptual modeling applications, UML, XML modeling, and industrial presentations.