DEXA 2004, the 15th International Conference on Database and Expert Systems Applications, was held August 30— September 3, 2004, at the University of Zaragoza, Spain. The quickly growing spectrum of database applications has led to the establisment of more specialized discussion platforms (DaWaK Conference, EC-Web Conference, EGOVConference, Trustbus Conference and DEXA Workshop: Every DEXA event has its own conference proceedings), which were held in parallel with the DEXA Conference also in Zaragoza. In your hands are the results of much effort. The work begins with the preparation of the submitted papers, which then go through the reviewing process. The accepted papers are revised to final versions by their authors and are then arranged within the conference program. All culminates in the conference itself. For this conference 304 papers were submitted, and I want to thank to all who contributed to it; they are the real base of the conference. The program committee and the supporting reviewers produced altogether 942 referee reports, in average 3,1 reports per paper, and selected 92 papers for presentation. At this point we would like to say many thanks to all the institutions that actively supported this conference and made it possible. These were: • University of Zaragoza • FAW • DEXA Association • Austrian Computer Society