This chapter explores the emergence (not always explicit), the uses and the misuses of proportionality analysis during a crucial period of Peruvian democracy: the transition of the 2000s, following the collapse of the Fujimori regime. The history of the principle of proportionality in Peru is associated to the development of judicial review and the expansion of constitutionalism. Its increasing presence in judicial reasoning reveals progress in terms of the effectiveness of constitutional rights and the defense of democratic institutions, but also an alarming trend toward its formalistic use. Since the Constitutional Tribunal has been the main actor behind this process, the chapter mainly focuses on its decisions, but some decisions by the Supreme Court and by administrative courts are also covered, given its recurrent use by the judiciary at large and its role in decentralized judicial review, especially in the context of ordinary criminal procedures where the legality of pretrial detention is examined.