Before contact with Europeans had begun, the native peoples of North America were varied in their demographic characteristics; nevertheless, available evidence indicates that, on an average, their life-expectancy-at-birth values fell into the same low ranges typical for other groups at similar levels of technological development. While the total population at contact is still unknown, political and cultural biases have generally forced estimates into artificially high or low ranges. There is general agreement that the shock of contact with invading Europeans led to substantial reductions among most aboriginal populations, but in North America some groups were much less disrupted than others. Many original populations disappeared altogether, but whether or not their demise was primarily a function of short-run, rapid disruption caused by disease and/or warfare, or a slower process spread out over several generations involving assimilation in its various forms, remains uncertain. With the establishment of the reservation system in the 19th century a basis was provided for continued demographic and cultural survival. By the early 20th century most reservation populations were beginning a demographic transition based on declining death rates and high fertility. For several generations rapid growth has continued. As urbanization increases recent fertility declines are expected to accelerate even further. Meanwhile the rapid urbanization of the surviving native peoples poses a real threat to their cultural distinctiveness. Finally, all phases of native American demographic history are characterized by defective and inadequate data which makes straightforward description or analysis perilous.