During the past half century, our knowledge of the continental crust and upper mantle of the United States has been significantly increased through geophysical observations. We here present a concise summary of the gross geophysical features of the crust and upper mantle, and highlight some of the historical developments that led to this knowledge. Velocity models derived from seismic observations can be related to the structure, composition, and rheologic properties of the crust and upper mantle and to important solid-to-solid phase transformations. Magnetic investigations, radioactive age dating, seismicity, and geological studies have revealed the worldwide patterns of sea-floor spreading, continental drift, and plate tectonics. Gravity, electrical, heat-flow, and stress measurements have been applied increasingly to studies of the continental lithosphere. Important regional similarities and differences have been discovered, and simple concepts of isostasy and crustal deformation have had to be modified or discarded. This memoir constitutes a comprehensive review and evaluation of these investigations.