The Sixth International Symposium on Spatial Databases (SSD'99) was held in Hong Kong, China, July 20-23, 1999. This is a \ten-year anniversary" edition. The series of conferences started in Santa Barbara in 1989 and
continued - annually in Zu ¨rich(1991),Singapore (1993),Portland,Maine (1995),and Berlin (1997). We are very pleased that on this occasion Oliver Gun ¨ ther, one of the initiators of the conference in 1989, agreed to give an
\anniversary talk" in which he presented his view of SSD in the past as well as in the future ten years. SSD is well established as the premier international conference devoted to the handling of spatial data in databases. The
number of submissions has been stable during the last years; in 1999 there were 55 research submissions, which is exactly the same number as for the last conference in Berlin. Out of these, the programcommittee accepted17
excellent papers for presentation.In addition to the \anniversary talk", the technical program contained two keynote presen- tions (Christos Papadimitriou, Timos Sellis), four tutorials (Markus Schneider, Leila De Floriani and
Enrico Puppo, Jayant Sharma, and Mike Freeston), and one panel. The papers included in these proceedings re?ect some of the current trends in spatial databases. Classical topics such as spatial indexing or spatial join
continue to be studied, as well as interesting new directions such as including generalization/scale in indexing or treating multiway instead of binary joins.