Imprisonment was one of the most important French colonial institutions in Senegal, but is the least studied by historians. With the Prison of Saint-Louis as a case study, my dissertation seeks to fill that deficit in the historiography. I explore the close ties between this prison, the development of the penitentiary, and colonization in Senegal, from the 1860s through the 1940s. This is not merely an institutional history. More importantly, I look at how the colonial enterprise influenced the mission assigned to imprisonment, and, conversely, how the situation inside the prison space impacted the relationships within the colonial society. I first deal with the evolution of the Prison of Saint-Louis and how it became a model for, and the nodal center of, the development of the penitentiary. Second, I analyze the internal operation of the prison in relation to the colonial policies. Lastly, I focus on the relationships within the 'prison society' and their connectedness with the 'free world'. My theoretical framework draws upon Foucault's and Rothman's works on the history of punishment in Europe and the United States, and the scholarship they inspired. I apply Lombroso's individualistic explanatory theories of criminality, more sociological ones such as Emile Durkheim's, and various colonialist ideologies. Finally, I borrow James Scott's concepts of the "weapons of the weak" and "infrapolitics of subordinate groups" to analyze the relationships within the prison space and their connection with the 'free world'. My sources are the abundant and largely untapped French colonial archives in the Archives du Senegal, including official records, newspapers, and various other colonial publications. I also use oral interviews. I studied some of these sources during my previous work, but only a full-length study like my dissertation could properly contextualize imprisonment within the larger frame of French colonialism in Senegal.