From Wikipedia: Saint Patrick's Day was made an official Christian feast day in the early 17th century and is observed by the Catholic Church, the Anglican Communion (especially the Church of Ireland),[4] the Eastern Orthodox Church, and the Lutheran Church. The day commemorates Saint Patrick and the arrival of Christianity in Ireland,[3] and celebrates the heritage and culture of the Irish in general.[5] Celebrations generally involve public parades and festivals, cèilidhs, and the wearing of green attire or shamrocks.[6] Christians also attend church services[5][7] and historically the Lenten restrictions on eating and drinking alcohol were lifted for the day, which encouraged and propagated the holiday's tradition of alcohol consumption.