Agriculture historically employed a large share of the overall population. For example, even in 1800, more than half the population in most European countries was working in agriculture. With the start of the industrial revolution and the accompanying mechanization, labor shifted out of agriculture. Still, throughout the 19th century and the beginning of the 20th century, increases in agricultural production were mainly driven by an increase in the growing area, whereas yields (output per area) were rather constant. This changed abruptly in the middle of the 20th century: yields have been increasing at a steady pace ever since. At the same time, inflation-adjusted agricultural commodity prices have been trending downward as increases in supply outpaced increases in demand. Food is an essential good, and while its price is currently low due to its abundance, it is responsible for a large consumer surplus given the highly inelastic demand. Understanding what factors contribute to the upward trend in yields is hence of first order importance for food security and human welfare. This book contains eight chapters that were presented at a NBER conference in May 2017. They examine in further detail what contributes to the remarkably steady increase in yields around the globe and assess whether this can continue into the future and whether it will impose significant environmental externalities. The book offers new innovative analyses using the methodological innovations as well as recently available micro-level data sets.