The constitutional structure of legal certainty is analyzed using the Brazilian Constitution as an example. The structure of the Constitution shows that legal certainty is an unequivocal positive principle, which protects it directly by "ensuring certainty" as a "right" and as a "value". Moreover, the Constitution also protects legal certainty in many of its dimensions, i.e., as certainty of law, before law, of rights, and as a right. The Constitution not only protects legal certainty in all of its manifestations but does so by assigning a high priority to legal certainty in the constitutional order. This is done through the way legal certainty is assured by the totality of the constitutional order and by its parts, through the insistence with which the Constitution protects legal certainty, through the independence of its foundations, and through the reciprocal efficacy of these same foundations. Finally, the Constitution protects legal certainty in favor of citizens and against the state.