This book demonstrates that American agricultural development was far more dynamic than generally portrayed. In the two centuries before World War II, a stream of biological innovations revolutionized the crop and livestock sectors, increasing both land and labor productivity. Biological innovations were essential for the movement of agriculture onto new lands with more extreme climates, for maintaining production in the face of evolving threats from pests, and for the creation of the modern livestock sector. These innovations established the foundation for the subsequent Green and Genetic Revolutions. The book challenges the misconceptions that, before the advent of hybrid corn, American farmers single-mindedly invested in labor-saving mechanical technologies and that biological technologies were static.