A significant number of the papers contributed by the authors of this effort were the outcome of research funded by the EU Chorochronos program.

We would like to thank the co-authors of our papers: P. Bozanis, S. Brakatsoulas, A. Corral, M. Egenhofer, C. Faloutsos, C. Gurret, Y. Karydis, N. Mamoulis, E. Nardelli, M. Nascimento, D. Papadias, D. Pfoser, G. Proietti, M. Ranganathan, P. Rigaux, J.R.O. Silva, M. Scholl, T. Sellis, E. Stefanakis, V. Vasaitis, M. Vassilakopoulos, and M. Vazirgiannis.

There are also several people who helped significantly in the preparation of this book. We take the opportunity to thank Antonio Corral for his contribution in approximate queries cost models for distance joins, and Elias Frentzos for his contribution in query optimization issues.

Finally, we would like to thank Catherine Drury and Michael Koy from Springer, for their great help and support toward the completion of this project. Their comments and suggestions were very helpful in improving the readability, organization, and overall view of the book.