During the last decades, old Celtic religion and traditions became increasingly popular again. Unlike other minor religious orientations, however, the Celtic does not separate itself from Christianity; it does not emphasise their differences but their similarities. On this basis, the symbiosis of Celtic Christianity is formed. This ability of adaption and assimilation is demonstrated throughout the Celtic history, particularly during the Roman Empire and Christianisation. The first part of this paper gives an overview of the old, pagan religion of the Celts with emphasis on the druids and similarities with Christianity. In the second part, the adaption to Roman and Christian religion is displayed along with a short presentation of the Irish Christianisation. The last part combines the previous ones by dealing with the survival and revival of Celtic religion and gives an insight of today’s Druidism.