This translation of Gwendolyn Cobb’s unrevised University of California dissertation is the first published version of a pioneering work written some thirty years ago on the economic history of early colonial Peru. Based entirely on a skillful analysis of published sources then available, it is now primarily of historiographical interest, for, although it remains a sound introduction to the history of Huancavelica and Potosí, it has been superseded in many areas by the subsequent archival researches of Guillermo Lohmann, Arthur Whitaker, Alberto Crespo, Josep Barriadas, and others. Introductory and concluding chapters on the general history of Potosí, divided at 1573, when mercury amalgamation was introduced there, are accompanied by a discussion of mercury mining at Huancavelica, and more detailed consideration of labor supply and provisioning for both mining centers, technology, and transportation of silver and mercury. A chapter on trade between Potosí and Buenos Aires before 1640 shows that even in this early period attempts to channel Upper Peru’s silver to Lima enjoyed only limited success.