The help and support of many people in Kenya and Germany made this dissertation possible. First, I am grateful to my supervisor Prof. Dr. Meike Wollni for encouraging me to pursue a Ph.D. and for always giving me valuable feedback when I needed it. A number of other people from the Department of Agricultural Economics and Rural Development at the University of Göttingen deserve my gratitude; Prof. Dr. Matin Qaim for co-supervising my dissertation, Prof. Dr. Achim Spiller for serving on the examination committee, and my colleagues and fellow doctoral students for their moral and professional support. In Kenya I received important support from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in Nairobi as well as the Kenyan Agricultural Research Institute (KARI) in Kakamega. At ICRISAT, I would like to thank Dr. Alastair Orr for his valuable help and his interest in my research topic and Dr. Christin Schipmann for her great hospitality and her survival tips. At KARI, I am indebted to Dr. Chrispus Oduori for providing me with crucial information on the KARI extension activities. I am furthermore indebted to Richard Shikuku from Kote Mtaani Health and Environment Concerns (KOMHEC), who helped me to contact the village groups and to better understand the research setting. I would also like to thank Catherine Kinyanjui, Hope Wandera, and Laura Ouma for being very skilled and reliable enumerators. I am furthermore deeply thankful to the farmers who patiently answered all my questions and revealed a lot of personal information to complete strangers. Finally, my time in Kenya would not have been such an unforgettable and great experience without all the inspiring and amazing people that I met in Nairobi, in Kisumu, and in the villages of Western Province. A large part of my doctoral studies was funded by the Dorothea Schlözer Scholarship Program at