The Scandinavian countries have become known for their low rates of imprisonment and relatively humane prison conditions. What, though, has made possible this model of imprisonment, so different from that of the Anglophone world? This article argues that contemporary Scandinavian prison policy has been the product of long-term socio-political forces and cultural values leading to three distinct phases of prison development: (1) 1870s–1930s: separate confinement, penance and the influence of Lutheran pastors in prison practice; (2) 1930s–1960s: welfare, medicalization and work; (3) 1970s–present: a tension between the ‘normalization’ of prison life against recent concerns with security. The article traces in the development and interplay of these three phases against the background of social, political and cultural change in Scandinavia.