Saint Patrick's Day, or the Feast of Saint Patrick, is a religious and cultural holiday held on March 17th and is the traditional death date of Saint Patrick (c. 385 – c. 461), the foremost Patron Saint of Ireland.

Patrick was born in late fourth century A.D. Great Britain, but as a teen was kidnapped by Irish raiders and held captive for about six years. During his captivity he became a devout Christian. He escaped and returned to Great Britain and after an angel told him in a dream to return to Ireland as a missionary, Patrick began religious training, a course of study that lasted more than 15 years.

Patrick began his mission to bring Christianity to the island of Ireland about 432 AD, according to the Saint Patrick Centre in Downpatrick, County Down, Ireland. The Centre resides next to Down Cathedral, the legendary saint's final resting place. By his death in 461, the island was almost entirely Christian.

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), the Eastern Orthodox Church, and the Lutheran Church. The day commemorates Saint Patrick and the arrival of Christianity in Ireland, and, by extension, celebrates the heritage and culture of the Irish in general.

St. Patrick's Day mythology blends 5th-century religious history with Irish folklore, featuring popular legends such as St. Patrick banishing snakes from Ireland and using the shamrock to explain the Holy Trinity. While rooted in the life of a real saint who spread Christianity in Ireland, many stories, including the snake banishment, are symbolic, with snakes representing pagan evil.