Regnans in Excelsis is a papal bull that Pope Pius V issued on 25 February 1570. It excommunicated Queen Elizabeth I of England, referring to her as "the pretended Queen of England and the servant of crime", declared her a heretic, and released her subjects from allegiance to her, even those who had "sworn oaths to her", and excommunicated any who obeyed her orders: "We charge and command all and singular the nobles, subjects, peoples and others afore said that they do not dare obey her orders, mandates and laws. Those who shall act to the contrary we include in the like sentence of excommunication."

The Ridolfi plot was a Catholic plot in 1571 to overthrow Queen Elizabeth I of England and replace her with Mary, Queen of Scots. The plot was hatched and planned by Roberto Ridolfi, an international banker who was able to travel between Brussels, Rome and Madrid to gather support without attracting too much suspicion.