This volume is the final result of the research project ''Micro growth model", that was sponsored by the Central Research Pool of Tilburg University, the Netherlands. Apart from the University Council for this important financial support, I owe Prof. Dr. Fiet Verheyen very much for the way in which he introduced me into scientific circles and for the way in which he supervised and stimulated my work. Dr. Jan de Jong and Peter Janssen C. E. , Technical University of Eindhoven, piloted me safely through the mathe matics of optimal control theory and removed some technical barriers. Their help was indispensable for the success of this project. I would also like to mention the kind support of Prof. Dr. Jack Kleijnen, who gave me many valuable hints on how to present the results of this project. In this way I was able to contact with several resear chers inside and outside the Netherlands. Most grateful I am to Prof. Dr. Charles Tapiero, Jerusalem University, who commented on important parts of this book in a constructive way and who suggested many subjects for further research. Also Mr. Geert Jan vsn Schijndel, Tilburg University, should be mentioned here, because he closely read the work and I appreciated his remarks and corrections very much. Many collea gues have contributed to the results of this research project in a direct or indirect way. Especially I should like to mention my contacts with Prof. Dr.