Duke of Leinster is a title in the Peerage of Ireland and the premier dukedom in that peerage. The subsidiary titles of the Duke of Leinster are: Marquess of Kildare (1761), Earl of Kildare (1316), Earl of Offaly (1761), Viscount Leinster, of Taplow in the County of Buckingham (1747), Baron of Offaly, Baron Offaly (1620) and Baron Kildare, of Kildare in the County of Kildare (1870). The viscounty of Leinster is in the Peerage of Great Britain, the barony of Kildare in the Peerage of the United Kingdom, and all other titles in the Peerage of Ireland. The courtesy title of the eldest son and heir of the Duke of Leinster is Marquess of Kildare. The Duke of Leinster is the head of the House of Kildare.

Irish, also known as Irish Gaelic or simply Gaelic, is a Goidelic language of the Insular Celtic branch of the Celtic language group, which is a part of the Indo-European language family. Irish is indigenous to the island of Ireland and was the population's first language until the 19th century, when English gradually became dominant, particularly in the last decades of the century. Today, Irish is still commonly spoken as a first language in areas of Ireland collectively known as the Gaeltacht, in which only 2% of Ireland's population lived in 2022.