Understanding the genetic origins and demographic history of Indian populations is important both for questions concerning the early settlement of Eurasia and more recent events, including the appearance of Indo-Aryan languages and settled agriculture in the subcontinent. Although there is general agreement that Indian caste and tribal populations share a common late Pleistocene maternal ancestry in India, some studies of the Y-chromosome markers have suggested a recent, substantial incursion from Central or West Eurasia. To investigate the origin of paternal lineages of Indian populations, 936 Y chromosomes, representing 32 tribal and 45 caste groups from all four major linguistic groups of India, were analyzed for 38 single-nucleotide polymorphic markers. Phylogeography of the major Y-chromosomal haplogroups in India, genetic distance, and admixture analyses all indicate that the recent external contribution to Dravidian- and Hindi-speaking caste groups has been low. The sharing of some Y-chromosomal haplogroups between Indian and Central Asian populations is most parsimoniously explained by a deep, common ancestry between the two regions, with diffusion of some Indian-specific lineages northward. The Y-chromosomal data consistently suggest a largely South Asian origin for Indian caste communities and therefore argue against any major influx, from regions north and west of India, of people associated either with the development of agriculture or the spread of the Indo-Aryan language family. The dyadic Y-chromosome composition of Tibeto-Burman speakers of India, however, can be attributed to a recent demographic process, which appears to have absorbed and overlain populations who previously spoke Austro-Asiatic languages.