Welcome to the "International Symposium on the Genetics and Exploitation of Heterosis in Crops." Heterosis has significantly increased the productivity and quality of major crops in our century, contributing additional food, feed, fiber, and other important products. Several short symposia on specific aspects of heterosis have been organized in the past, but this is first time in nearly 50 years that some 450 scientists from more than 60 nations gather to discuss the subject in depth. Among other topics, this event will cover the genetic, physiological, biochemical, and molecular mechanisms underlying hybrid vigor; appropriate germplasm and breeding methodologies; and commercial strategies and methodologies for maximum and sustainable utilization of heterosis. The Book ofAbstracts provides descriptions of nearly 200 scientific presentations dealing with recent research on heterosis. The abstracts are extended; that is, they are intended to provide the reader with relevant details on materials and methods, results, and conclusions of the studies. Most are for posters presented at the symposium, in which case the title carries the corresponding code assigned to the poster. Abstracts of presentations by invited speakers are also included; full text versions will be published soon after the symposium in a proceedings by the American Society of Agronomy. We are grateful to CIMMYT scientists M. Barandiaran, D. Beck, J. Betran, N. Bohorova, ,S. Castellanos, H. Córdova, M. Kazi, S. Pandey, F. San Vicente, G. Srinivasan, W. Pfeiffer, and M. van Ginkel, who carefully reviewed the abstracts for scientific quality and value. We also thank CIMMYT science writer M. Listman for editing, formating, and overseeing production of this book. We have modified the abstracts for space, content, and clarity in many cases, but authors are still ultimately responsible for the quality of their submissions.354 pages