The right to freedom of religion, as all over fundamental rights, benefits the prisoner, in the limit of inherent contingencies in custody. The protection of freedom of religion suffers first from its confrontation with the requirements due to security and the good order of the establishment. On the other hand, in the specific context of deprivation of liberty, only the recognition of a positive obligation in the responsibility of the state to organise the religious worship in prison is likely to not reduce the prisoner’s religious freedom too much. The protection of freedom of religion could suffer from its confrontation with the imperatives of neutrality of the public service and secularism. The positive obligation emerges from case law, even if its intensity is contrasted, depending on the sector of religious freedom concerned.