The Twelfth is a primarily Ulster Protestant celebration held on 12 July. It began in the late 18th century in Ulster. It celebrates the Glorious Revolution (1688) and victory of Protestant King William of Orange over Catholic King James II at the Battle of the Boyne (1690), which ensured a Protestant Ascendancy in Ireland. On and around the Twelfth, large parades are held by the Orange Order and Ulster loyalist marching bands, streets are plastered with union jacks and bunting, and large towering bonfires are lit in loyalist neighbourhoods. Today the Twelfth is mainly celebrated in Northern Ireland, where it is a public holiday, but smaller celebrations are held in other countries where Orange lodges have been set up.

The Battle of the Boyne took place in 1690 between the forces of the deposed King James II, and those of King William III who, with his wife Queen Mary II, had acceded to the Crowns of England and Scotland in 1689. The battle was fought across the River Boyne close to the town of Drogheda in the Kingdom of Ireland, modern-day Republic of Ireland, and resulted in a victory for William. This turned the tide in James's failed attempt to regain the British crown and ultimately aided in ensuring the continued Protestant ascendancy in Ireland.