Editorial introduction © 2007 The Authors. Journal compilation © 2007 VVS. Published by Blackwell Publishing, 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA. 1 Statistica Neerlandica (2007) Vol. 61, nr. 1, pp. 1–3 Editorial introduction Antoon Kolen passed away on October 3, 2004 at the much too young age of 51. We had the privilege of being his first PhD students in the mid-1980s. This was at the Econometric Institute of Erasmus University Rotterdam, where Antoon had been working since finishing his PhD research at the CWI in Amsterdam. Not long after we had started our research, Antoon moved to Maastricht University to form and head the operations research group at the Department of Quantitative Economics. Nevertheless, he remained committed to supervising us. Throughout the years, until the very end of his life, others who worked with him would have similar experiences. Enthusiasm for and commitment to research best typify Antoon’s professional career. This special issue of Statistica Neerlandica contains contributions of people who collaborated with Antoon at one of the aforementioned universities. It shows their love and respect for Antoon, both as a researcher and as a person. It also illustrates the variety of research topics that Antoon was inter- ested in and the influence that he had, directly or indirectly, on the development of our profession. Moreover, we are very proud to publish in this special issue Antoon’s last article, which is based on an almost finished manuscript that he left behind. Stan van Hoesel, Albert Wagelmans 2 Editorial Selected publications of Antoon Kolen Kolen, A. (1982), Location problems on trees and in the rectilinear plane, PhD dissertation, Mathematisch Centrum, Amsterdam, the Netherlands. Hoffman, A., A. W. J. Kolen and M. Sakarovitch (1985), Totally balanced and greedy matrices, SIAM Journal of Algebraic Discrete Methods 6, 721–730. Kolen, A.W. J., A. H. G. Rinnooy Kan and H. W. J. M.