Christianity in the form of both Roman Catholicism and Protestantism is the most widely practised religion in Ireland. Christianity was brought to Ireland during or prior to the 5th century and its early history among the Irish is in particular associated with Saint Patrick, who is generally considered Ireland's patron saint. The Celtic festival of Samhain, known as Halloween, originated in Ireland and is now celebrated all over the world. Source:https://en.wikipedia.org/wiki/Culture_of_Ireland