The rise of autonomous institutions out of the three traditional branches is a worldwide tendency. The phenomenon is especially pervasive in Brazil, whose legal system grants autonomy to oversight bodies, regulatory agencies and other entities. Although these institutions are invested with prerogatives such as the sole authority to manage their financial and human resources and the right to elaborate their mandatory budgets, the degree of autonomy they hold varies considerably. While oversight bodies have achieved a high level of autonomy in Brazil, regulatory agencies repeatedly suffer from undue interference. Yet, entities as the Central Bank lack formal legal autonomy, but are almost immune to interventions. The paper reveals that, while important, normative provisions may sometimes be not enough nor, at other times, necessary to assure independence. Political or conventional factors are just as or even more important in determining the autonomy effectively held by public entities.