The foundations for this thesis were laid during the work on the Interreg IIc project named EURBANET in which I participated between 2000 and 2002. This project focused on four polycentric urban regions in North West Europe and explored the practical value of this kind of a region as a planning concept. The subject of polycentric urban regions caught my great personal interest and it was only a matter of course that such regions would become the focus of my PhD research, the EURBANET project providing a jump-start.

Although writing a PhD thesis is foremost meant to be a demonstration of an individual's capability of doing academic research, it could not have been accomplished without the help of others. This holds particularly for professor Hugo Priemus and dr. Marjolein Spaans. Both Hugo and Marjolein have accurately read, discussed and commented on numerous versions of research papers, not only those that are included in this thesis. I feel privileged to have such an experienced and distinguished promoter as Hugo Priemus. Many thanks for the efforts to get my research proposal funded, but above all for sharing your experience in doing academic research and of the rigors of getting published with me. In addition, I greatly value the relative freedom – as I experienced it – I was given to further develop the research as a sign of having confidence in a good ending. Marjolein is to be credited for making the process of doing PhD research have many ‘ups’ and few ‘downs’. Many thanks for putting me on the track, for keeping me there and for safeguarding my interest in the process.

The members of the OTB-department of Urban and Regional Development should be credited for the pleasant, harmonious and stimulating working atmosphere. Next to the occasional chat over coffee or lunch, for me, this also includes the well-established academic orientation of our work. Thanks to the department co-ordinators Robert Kloosterman, Wil Zonneveld and Kees Maat for safeguarding this. Special thanks goes to Arie Romein, who co-authored one of the papers in this thesis. The publication of this paper has very much encouraged me to proceed in writing a thesis based on a collection of papers. I also very much enjoyed working with him and my other colleagues Bart Lambregts, Bas Waterhout, Dominic Stead, Eric Hoppenbrouwer and Wil Zonneveld on several international research projects within the frameworks of Interreg IIc and ESPON, as well as the NOVEM-project on integral policy making. Working on these projects meant a welcome distraction from the PhD research and allowed for a much richer research experience.

OTB Research Institute for Housing, Urban and Mobility Studies provides researchers with many opportunities and few constraints. Important for me in particular was the opportunity to pursue research on issues that were driven by my own personal interests, as well as according to their theoretical and practical relevance. I am indebted to many people in the institute who have contributed in some way to the completion of this thesis. I very much appreciated the comments and advice of the late Frans Dieleman. Thanks go to Henny Coolen and Sylvia Jansen for their methodological advice and to Herman Toneman for drawing up several figures. Roommates are important in making a nice working atmosphere. In that sense I owe much to Eric Hoppenbrouwer, Reinout Kleinhans and now Wendy Bohte for the fun, interest and encouragement.

Help was also provided by people outside OTB Research Institute for Housing, Urban and Mobility Studies. This includes the participants in the EURBANET project as Chapter 5 builds on its results. Thanks go to the managers of hospitals and universities for professional education for their willingness to be interviewed for parts of the field research. In addition, many organisations have been willing to provide me with data and figures. Peter Schmitt assisted greatly in acquiring German data. Rachel Heap skilfully and accurately edited my English.

No research without funding. Funding for this research was kindly provided by the Dutch government through the Habiforum Program Innovative Land Use and by Delft University of Technology through the Delft Centre for Sustainable Urban Areas. Furthermore, I acknowledge the financial assistance for purchasing data by the Deltametropolis Association.

Enjoying the warmth and support of my parents, sister, ‘in-laws’ and friends has been very important to me. Special thanks goes to Joris Bekkers and Martijn van Berkum for their support as paranimfs. Immeasurable thanks and love go to my pillar in life, Lonneke. Being with you, and our children, is a wonderful experience that I value dearly. Finally, Veerle, Casper and Wessel; while your actual geographical worlds are still so small, learning about other countries and peoples brings the most magical associations and great fantasies. I sincerely hope that when we explore our world together, or you on your own, you will enjoy and care for what is out there.