Saint Patrick, 387 – 493, was a Romano-Briton and Christian missionary, who is the most generally recognised patron saint of Ireland. It has been implied that he lived from 340 to 440, and ministered in what is modern day Northern Ireland from 428 onwards. The dates of Patrick's life cannot be fixed with certainty, but on a widespread interpretation he was active as a missionary in Ireland during the second half of the fifth century.

Two authentic letters from him survive, from which come the only universally accepted details of his life. When he was about 14 he was captured from Britain by Irish raiders and taken as a slave to Ireland, where he lived for six years before escaping and returning to his family. After entering the Church, he returned to Ireland as an ordained bishop in the north and west of the island, but little is known about the places where he worked. By the eighth century he had come to be revered as the patron saint of Ireland. Saint Patrick’s Day, March 17th, is celebrated both in and outside of Ireland, as both a liturgical and non-liturgical holiday.

Green ribbons and shamrocks were worn in celebration of St Patrick's Day as early as the 17th century. He is said to have used the shamrock, a three-leaved plant, to explain the Holy Trinity to the pre-Christian Irish, and the wearing and display of shamrocks and shamrock-inspired designs have become a ubiquitous feature of the day. The phrase "the wearing of the green", meaning to wear a shamrock on one's clothing, derives from the song of the same name.

This vintage image shows a young Irish Lass with a large wicker basket on her back overflowing with shamrocks.