This book would not have been possible without the tremendous help of many colleagues and friends. I started to work on questions of social interactions and fertility during my dissertation at the University of California at Berkeley. I am greatly indebted to Ronald D. Lee and Kenneth W. Wachter, who introduced me to demography and economic demography and who provided invaluable comments and support during my dissertation. I am also grateful to Daniel McFadden and Paul Romer for many comments and suggestions during my years in Berkeley. Since my dissertation, I have intensively collaborated with Susan Watkins and Jere Behrman on empirical analyses of social networks and fertility, using the Kenyan Diffusion and Ideational Change (KDIC) data. This collaboration has been very joyful and fruitful, and it has provided a great inspiration for my thinking on the topic of social interactions and fertility. I am indebted to both for their insights and support during the recent years. Numerous other friends, colleagues, and participants at seminars or conferences have also provided tremendous help during the writing of this book. Finally, this research would not have been possible without the generous support of the SSRC-MacArthur Foundation Fellowship, the TransCoop Program of the German American Academic Council, the International Institute for Applied Systems Analysis, and the Max Planck Institute for Demographic Research.
Some of the chapters in this book build on material that I have previously published in professional journals, in part in collaboration with Susan C. Watkins and Jere R. Behrman. The interested reader may wish to refer to some of the following articles: 'Learning in Social Networks and Contraceptive Choice' (Demography 34(3), 1997, pp. 369-383); 'Social Interaction and Fluctuations in Birth Rates' (Population Studies 54(2), 2000, pp. 223-238); 'Fertility Decline as a Coordination Problem' (Journal of Development Economics 63(2), 2000, pp. 231-263); 'Empirical Assessments of Social Networks, Fertility and Family Planning Programs: Nonlinearities and their Implications' (Demographic Research 3(7), 2000, with Jere R. Behrman and Susan C. Watkins); 'The Density