The sixth International Conference on Enterprise Information Systems (ICEIS) held in Porto in 2004, brought together researchers, engineers and practitioners interested in the advances and business applications of information systems. It is now the largest Conference in Europe in the area of Information Systems, and one of the most demanding with only 15% of the submissions accepted as full papers. The papers selected in this book are selected from the different aspect covered at the conference including Databases and Information Systems Integration, Artificial Intelligence and Decision Support Systems, Information Systems Analysis and Specification, Software Agents and Internet Computing and Human-Computer Interaction.