Little did I realize when I first read Woodrow Borah's New Spain's Century of Depression in 1962 that I would begin a search for similar material for the Andean area of South America that would continue for almost two decades. Borah's description of the relationship between population and economy in Central Mexico stimulated my investigation for parallel patterns in Peru. While preparing my master's thesis, under the direction of Lyle N. McAlister at the University of Florida, I became aware of the limited knowledge of the dynamics of population change in colonial Peru. By 1969 I had completed much of the basic research on Peru's Indian population from 1570 to 1620 for my dissertation at the University of Texas with Thomas F. McGann and James Lockhart, but teaching duties, and revisions, led to a delay in completion until 1973. I have continued the search for supplementary materials since that date, conducting new research in Peru in 1973, 1974, and finally 1977. I have now reached the point where I feel continued investigation would provide only diminishing returns. Most of the population data for Indian Peru for the period prior to 1650 have already been collected. Census results, at least the totals, for almost 585 repartimientos – the primary local unit of Indian administration – for various dates provide the basis for the presentstudy. Undoubtedly, other information will be found, but it is unlikely that the data base will be substantially modified. Many people have assisted me during the course of research and writing. Woodrow Borah and William Denevan have read a draft of the present volume. I owe them special thanks for their comments and support.