This chapter examines a relatively underexplored period in Brazilian criminology, outlining the main schools of thought that have shaped – and perhaps continue to shape – the perspectives of jurists, physicians, criminologists, and penitentiary officials involved in defining forms of social control validated by scientific-medical discourse. Medical-criminological knowledge extended beyond the scientific domain, taking on a normative and prescriptive role in shaping social control policies in Brazil. Under the guise of modernisation and progress, scientific practices were utilised to reinforce narratives of exclusion and discipline, thereby consolidating a legal and institutional culture characterised by selectivity and the racialisation of crime control. Within this framework, eugenics emerged as a scientific, political, and social movement advocating for the regulation of human reproduction to enhance national and racial characteristics, with the aim of addressing not only physical diseases but also various social issues perceived as barriers to progress, such as crime. This chapter seeks to elucidate how these dynamics influenced the Brazilian punitive imagination and practices, contributing to a deeper understanding of the intersections between science, cultural power, and exclusion in the country's social history.