Essays in Population History: Mexico and California, Volume Three is the final volume of the Cook and Borah Essays, marking the conclusion of the collaborative work of Sherburne F. Cook, who passed away in 1974. This volume features three essays that continue the research into the impact of European contact on indigenous populations, a theme central to Cook’s academic work. The first chapter focuses on determining the low point of the indigenous population of central Mexico, illustrating the dramatic population decline following the Spanish Conquest. The chapter draws from a key document that not only provides demographic data but also sheds light on the royal fiscal system, contributing to a deeper understanding of Mexico's colonial-era administration. The second chapter revisits the socio-economic conditions of central Mexico during the sixteenth and early seventeenth centuries, particularly food production and nutrition. This essay builds on earlier anthropological studies and offers a revised theory on the widespread undernutrition experienced by the majority of the population. The final chapter shifts the focus to northern California, where Cook had long wished to apply the demographic analysis techniques used for Mexican materials. This chapter examines the registers of eight northern California missions, providing a truncated but insightful exploration of the impact of European colonization on the Costanoan Indians and other groups in the region. Although the study was not completed, it lays the groundwork for further research into the functioning of the California missions and their demographic effects. This volume, while concluding Cook’s work, also opens the door for future scholars to expand upon these findings. This title is part of UC Press's Voices Revived program, which commemorates University of California Press’s mission to seek out and cultivate the brightest minds and give them voice, reach, and impact. Drawing on a backlist dating to 1893, Voices Revived makes high-quality, peer-reviewed scholarship accessible once again using print-on-demand technology. This title was originally published in 1979.