The Brittany Campaign, or the Campaign of Brittany, was a military occupation of the Brittany, France, by Spain. It began in summer 1590 when Philippe-Emmanuel de Lorraine, Duke of Mercœur, the governor of Brittany, offered the port of Blavet to King Philip II of Spain so that he could harbour his fleet. The occupation formally ended on May 2, 1598, with the Peace of Vervins.

The Catholic League of France, sometimes referred to by contemporary Catholics as the Holy League, was a major participant in the French Wars of Religion. The League, founded and led by Henry I, Duke of Guise, intended the eradication of Protestantism from Catholic France, as well as the replacement of the French King Henry III, who had acquiesced to Protestant worship in the Edict of Beaulieu (1576). The League also fought against Henry of Navarre, the Protestant prince who became presumptive heir to the French throne in 1584.