This chapter presents the historical background and current organisation of religion in the Danish penitentiary system from a legal and sociological perspective. The role and presence of religion in prison were not much discussed until 2006, when the Prison and Probation Service published its first report on religion in prisons. Nevertheless, the Lutheran prison chaplain has been a natural part of the Danish prison system since the establishment of the modern prison in the nineteenth century. Following this historical background, the regulation of religion in prison is presented to show the national and international legal framework regulating the work of chaplains and religious practices of inmates. The Prison and Probation Service produces much information and many statistics on prison life, but not related to religion. The final section presents empirical studies of religion among inmates, showing, for instance, that the proportion of Muslim inmates was the same in 2006 and 2017. Although the proportion was around 20% there are very few Muslim chaplains in prison, and they are a relatively recent addition to Lutheran chaplains from the majority church. The last section examines the majority church chaplains, and shows that they take it upon themselves to cater to the needs of all inmates. Although imams remain contested in the wider society, The Prison and Probation Service welcomes Muslim Chaplaincy (after thorough vetting) because they can oppose potential radicalisation and provide pastoral care to the inmates.