In recent years, scholars have noted the rise of a particular type of authoritarianism worldwide, in which rulers manipulate institutions designed to implement the rule of law so that they instead facilitate the exercise of arbitrary power. Even as scholars puzzle over this seemingly new phenomenon, scholarship on African politics offers helpful answers. This book places literature on the post-colonial African state in conversation with literature on modern authoritarianism, using this to frame over ten months of qualitative field research on Uganda's informal security actors - including vigilante groups, local militias, and community police. Based on this research, the book presents an original framework - called 'institutionalized arbitrariness' - to explain how modern authoritarian rulers project arbitrary power even in environments of relatively functional state institutions, checks and balances and the rule of law. In regimes characterized by institutionalized arbitrariness, the state's stochastic assertions and withdrawals of power inject unpredictability into the political relationship between both local authorities and citizens. This arrangement makes it difficult for citizens to predict which authority, if any, will claim jurisdiction in a given scenario, and what rules will apply. This environment of pervasive political unpredictability limits space for collective action and political claim-making, while keeping citizens marginally engaged in the democratic process. The book is grounded in empirical research and literature theorizing the African state, while seeking to inform a broader debate about contemporary forms of authoritarianism, state-building, and state consolidation.