During my PhD-studies I experienced the support of many people to whom
I feel deeply indepted.

CRNI 2008 (1) I am very grateful and would like to thank Pio Baake, Bernhard
Bukovc, Christian Wey, G\'{e}za S\'{a}pi, Matthias Finger and Rolf K\"{u}%
nneke for very valuable and helpful comments and suggestions. The paper also
benefited from presentations at the DIW Berlin IGW research seminar and the
conference \textquotedblleft Competition and Regulation in Network
Industries\textquotedblright\ (Brussels, 2008). Financial support from the
International Post Corporation for the research project \textquotedblleft
Economics and Regulation of the Postal Industry\textquotedblright\ is
gratefully acknowledged.

DIW\ GC, IPC, CRRI, CRNI, Lausanne

BSP\ VANESSA\ First and forefost, I would like to thank Christian Wey who
provided me with the opportunity to develop my own interests in the field of
industrial organization. He was never tired to support and motivate me. I
would also like to thank the committee members, Frank Heinemann and Dorothea
K\"{u}bler, for their valuable comments. Special thanks go to Pio Baake
whose guidance was very important for my academic development. With his
motivation and his patience he introduced me to the world of research. In
particular, I would like to thank him for his support in the difficult
moments of my thesis.

I would like to thank Vincent R\'{e}quillart, St\'{e}phane Caprice, and
Fabian Berg\`{e}s-Sennou for helpful discussions at the very beginning of my
thesis and the opportunity to spend six inspiring months at the Toulouse
School of Economics. Financial support from the Federal State of Berlin and
the DAAD is also gratefully acknowledged.

This thesis would not have been possible without G\"{u}nter Lorenzl, the
supervisor of my diploma thesis in agricultural economics, as he encouraged
me to write my doctoral thesis in industrial organization. He also provided
me with the most interesting and exiting literature beyond academic papers I
read during this time.

I especially want to thank Sven Heitzler who shared not only the office and
the coffee machine with me but also his immense knowledge on computer
matters. I am grateful to Sibylle Kremser who took care of all
administrative issues throughout my time at the DIW Berlin. In addition I
would like to thank my collegues, Georg Erber, Katja Frank, Kurt Geppert,
Martin Gornig, Kornelia Hagen, Nicola Jentzsch, Daniel Nepelski, Manfred
Schmidt, and Irina Suleymanova, for the enjoyable time I spent at the DIW
Berlin.

All in all, my thanks go to my personal friends among them Gisa Gerold, Maxi
H\"{o}nigschmid, Silke H\"{u}ttel, Till Vielrose, and Alexander von Nell for
the many nice moments we spent together. I am deeply indebted to R\"{u}diger
Haspl. His encouragement and love was essential for me while writing this
thesis. Most importantly, my parents deserve all my deepest thanks. During
the years of my education they supported me through the ups and downs. I
would like to dedicate this thesis to them.