The Union of Arras (Dutch: Unie van Atrecht, French: Union d'Arras, Spanish: Unión de Arrás) was an alliance between the County of Artois, the County of Hainaut and the city of Douai in the Habsburg Netherlands in early 1579 during the Eighty Years' War. Dissatisfied with the religious policies of rebel leader Prince of Orange and the States General of the Netherlands, and especially the rise of the radical Calvinist Republic of Ghent since October 1577, they signed a declaration on 6 January 1579 about their intent to offer a vigorous defense of the Roman Catholic religion against what they saw as encroachments by Calvinists in other provinces. These signatories would begin negotiations for a separate peace with the Spanish Crown, which resulted in the Peace Treaty of Arras of 17 May 1579.