H.L.A Hart legal positivism offers answers to the fundamental question about the concept of law with a very sophisticated formulation, involving the union of primary and secondary rules. Among the most relevant aspects of the developed model, at its core rests the (ultimate) rule of recognition, a secondary rule designed as a solution to the problem of uncertainty, stemming from the difficulty of identifying which rules belong to the community s legal system and their scope of application. The purpose of this study is, from the theoretical framework developed by Hart in The Concept of Law, to work in the interface between the legal theory and the constitutional law, and to apply the hartian theory to the Brazilian legal phenomenon. Thus, the first two chapters will address conceptual issues regarding the rule of recognition institute, identifying some problems in its canonical reading, and will culminate with the proposal of a new understanding of the institute, one that places the people in the relevant recognitional group. Finally, at the fourth chapter, there will be an attempt to describe the ultimate rule of recognition of Brazilian law, considering the current relevant practices of the Brazilian legal and politic community in identifying the law.