Indonesia, an island nation linking mainland Asia with the Pacific world, hosts a wide range of linguistic, ethnic and genetic diversity. Despite the complexity of this cultural environment, genetic studies in Indonesia remain surprisingly sparse. Here, we report mitochondrial DNA (mtDNA) and associated Y-chromosome diversity for the largest cohort of Indonesians examined to date-2740 individuals from 70 communities spanning 12 islands across the breadth of the Indonesian archipelago. We reconstruct 50 000 years of population movements, from mitochondrial lineages reflecting the very earliest settlers in island southeast Asia, to Neolithic population dispersals. Historic contacts from Chinese, Indians, Arabs and Europeans comprise a noticeable fraction of Y-chromosome variation, but are not reflected in the maternally inherited mtDNA. While this historic immigration favored men, patterns of genetic diversity show that women moved more widely in earlier times. However, measures of population differentiation signal that Indonesian communities are trending away from the matri- or ambilocality of early Austronesian societies toward the more common practice of patrilocal residence today. Such sex-specific dispersal patterns remain even after correcting for the different mutation rates of mtDNA and the Y chromosome. This detailed palimpsest of Indonesian genetic diversity is a direct outcome of the region's complex history of immigration, transitory migrants and populations that have endured in situ since the region's first settlement.