This book emerges from the thinking, discussing, scrutinizing, writing and working of several people. It is partly because of each of their efforts that this book and the project has reached this progress and is still making further improvement.

First, I would like to thank the researchers of the PKS project: Drs. Mirjam R.J. Bouwens, for perfect assistance during several years; I'm glad you learned a lot and wish you luck with your other ambitions; Drs. Leo M.J.J. Wagemans, for being a fine colleague and most of all for being constantly aware of the concrete problems of the Open University, reminding us to these, and avoiding us to do 'theoretical' and 'strictly experimental' research; Dr. Martin M.A. Valcke, for being a great expert, much greater than 'others'; Dirk W. Niestadt, for being a flashing, weekend-working and 'crashing' assistant - the IBM 386 was much too slow for his capacities; Drs. Rob E.J. Koper for his critical contributions to this work and his revealing input in our 'mastermind and risk' evenings; Drs. Mieke Steenbakkers, Marcel Kemper and Vivian Gorissen for their assistance as pioneers.

Also a special word for the external referees of the Universities of Heerlen and Maastricht and STOHO Brussels: Drs. Frank De Langen, Prof. Dr. Dick Feenstra, Prof. Dr. Henk Peer, Dr. Steve Foster, Drs. Mien S.R. Segers, Dr. Maurice de Volder.

Thanks also to the OTIC researchers of the section 'intake, guidance and evaluation' who participated in discussions and all those that encouraged in one or another way. Also to Dr. Paul A. Kirschner and PKText Inc. Consultancy for breaking grounds.

Further, I would like to thank those who have contributed to this work by means of their support, their comments (sometimes in the distance teaching spirit by means of correspondence) or discussions on different topics:

Prof. Dr. Patricia Alexander (on prior knowledge research), Prof. Dr. Ference Marton, Dr. Thomas Kroksmark, Dr. Björn Hasselgren and Drs. Elisabeth Nyqvist (on qualitative research), Prof. Dr. Lennart Sjöberg and Dr. Britt-Marie Drottz (on research at Stockholm and Brussels School of Economics), Prof. Dr. Gilberte Schuyten and Dr. Gudrun Balke (on data-analysis), Prof. H. de Wolf, Prof. W. Wijnen and Prof. E. De Corte (for their critical comments).

Finally, many thanks to Mien who is my wife, my lover and my manager. Without her management (and the rest) it would have been hardly possible.

To Niklas, my dearest son; sorry for all the times I did not play and had no time to tell stories. Nevertheless, you learned to play computergames very well.

To Esben, my other dearest son; sorry for forcing you to play with things you did not want to and for my disturbed attention.

To Vjara, my darling young one, who is now 'close to the sun'.