The words Popery and Papism are mainly historical pejorative words in the English language for Roman Catholicism, once frequently used by Protestants and Eastern Orthodox Christians to label their Roman Catholic opponents, who differed from them in accepting the authority of the Pope over the Christian Church. The words were popularised during the English Reformation (1532–1559), when the Church of England broke away from the Roman Catholic Church and divisions emerged between those who rejected papal authority and those who continued to follow Rome. The words are recognised as pejorative; they have been in widespread use in Protestant writings until the mid-nineteenth century, including use in some laws that remain in force in the United Kingdom.

Anti-Catholicism is hostility towards Catholics and opposition to the Catholic Church, its clergy, and its adherents. At various points after the Reformation, some majority-Protestant states, including England, Northern Ireland, Prussia, Scotland, and the United States, turned anti-Catholicism, opposition to the authority of Catholic clergy (anti-clericalism), opposition to the authority of the pope (anti-papalism), mockery of Catholic rituals, and opposition to Catholic adherents into major political themes and policies of religious discrimination and religious persecution. Major examples of groups that have targeted Catholics in recent history include Ulster loyalists in Northern Ireland during the Troubles and the second Ku Klux Klan in the United States. The anti-Catholic sentiment which resulted from this trend frequently led to religious discrimination against Catholic communities and individuals and it occasionally led to the religious persecution of them. Historian John Wolffe identifies four types of anti-Catholicism: constitutional-national, theological, popular and socio-cultural.