This book examines the relationship between indigenous populations in the north-central highlands of Ecuador and disease, especially those infections introduced by Europeans during the sixteenth century. Disease, of course, existed in the Americas long before 1500. But just as native societies resisted and eventually adapted to European conquest, so too did they adapt to Old World pathogens. Just as the responses of Indian communities to the economic and political demands of Spaniards varied over time, so too did the immunological responses of indigenous populations change over generations. What began in the sixteenth century as contact and invasion soon would involve both Indians and Europeans in a new history of biological, as well as social, adaptation.