Saint Patrick's Day (Lá ’le Pádraig or Lá Fhéile Pádraig), colloquially St. Paddy's Day or Paddy's Day, is an annual feast day which celebrates Saint Patrick (circa 385-461 AD), one of the patron saints of Ireland, and is generally celebrated on March 17.

The day is the national holiday of Ireland. It is a bank holiday in Northern Ireland, and a public holiday in the Republic of Ireland, Montserrat, and the Canadian province of Newfoundland and Labrador. In the rest of Canada, the United Kingdom, Australia, the United States and New Zealand, it is widely celebrated but is not an official holiday.

It became a feast day in the Roman Catholic Church due to the influence of the Waterford-born Franciscan scholar Luke Wadding in the early part of the 17th century, and is a holy day of obligation for Roman Catholics in Ireland. The date of the feast is occasionally moved by church authorities when March 17 falls during Holy Week; this last happened in 1940 when Saint Patrick's Day was observed on 3 April in order to avoid it coinciding with Palm Sunday, and will happen again in 2008, when it shall be held on either March 14 or March 15. After 2008, March 17th will not fall during Holy Week again until 2160.