Database research is a field of computer science where theory meets applications. Many concepts and methods, that were regarded as issues of theoretical interest when initially proposed, are now included in implemented database systems and related products. Examples abound in the fields of database design, query languages, query optimization, concurrency control, statistical databases, and many others. The papers contained in this volume were presented at ICDT’99, the 7th - ternational Conference on Database Theory, in Jerusalem, Israel, January 10–12, 1999. ICDT is an international forum for research on the principles of database systems. It is a biennial conference, and has a tradition of being held in beau- ful European sites: Rome in 1986, Bruges in 1988, Paris in 1990, Berlin in 1992, Prague in 1995, and Delphi in 1997. From 1992, ICDT has been merged with another series of conferences on theoretical aspects of database systems, The Symposium on Mathematical Fundamentals of Database Systems (MFDBS), that was initiated in Dresden (1987), and continued in Visegrad (1989) and Rosk (1991). ICDT aims to enhance the exchange of ideas and cooperation in database research both within unified Europe, and between Europe and the other continents. ICDT’99 was organized in cooperation with: ACM Special Interest Group on Management of Data (Sigmod) IEEE Israel Chapter ILA — The Israel Association for Information Processing EDBT Foundation ICDT’99 was sponsored by: The Hebrew University of Jerusalem Tel Aviv University Tandem Labs Israel, a Compaq Company This volume contains 26 technical papers selected from 89 submissions.