This Introduction identifies Eastern’s puzzling position in the landscape of nineteenth-century prisons: one of a few prisons, and then the only prison, to use a system of long-term solitary confinement. This chapter explores the historiography of Eastern and the early prisons looking for answers to the question of why one prison alone would continue to use a highly criticized mode of confinement? Turning to organizational theory, we find an answer in Philip Selznick’s “old” institutional theory. This chapter then identifies some of the ways in which a unique prison’s history helps us better understand the development of nineteenth-century prisons and penal change more generally. It concludes with some methodological notes.