Why do some dictatorships establish institutions typically associated with democracy, such as legislatures or political parties? We propose a new theoretical model of authoritarian power-sharing and institutions in dictatorships. We argue that political institutions in dictatorships enhance the stability of power-sharing, and therefore the survival of these regimes. However, authoritarian power-sharing through institutions is feasible only when it is backed by the crude but credible threat of a rebellion by the ruler's allies. Whereas the allies' political opportunities -- rather than a contingent
coordination of beliefs among them -- determine the credibility of their rebellion, institutions resolve the commitment and monitoring problems caused by the secrecy in authoritarian governance. Our theory generates new predictions about the empirical relationship between political institutions, economic development, and leader tenure.