Since the mid-1970s, the hundreds of American Indian reservations in the United States have been afforded substantial powers of self-government –from law enforcement and taxation to environmental and business regulation. The result has been a set of diverse efforts to overcome widespread poverty, with equally diverse outcomes. This study reports the results of research into the sources of development success during the “take-off” stage of self-government. Little evidence is found to support hypotheses that resource or human capital endowments hold keys to launching Indian economies. Instead, tribal constitutional forms appear to be make-or-break keys to development. Development takes hold when these forms provide for separations of powers and when their structures match indigenous norms of political legitimacy