Religious intolerance is intolerance against another's religious beliefs or practices or lack thereof.
The mere statement on the part of a religion that its own beliefs and practices are correct and any contrary beliefs are incorrect does not in itself constitute intolerance (i.e., ideological intolerance).
Religious intolerance, rather, is when a group (e.g., a society, religious group, non-religious group) specifically refuses to tolerate practices, persons or beliefs on religious grounds.
According to the 19th century British historian Arnold Toynbee, for a religious establishment to persecute another religion for being "wrong" ironically puts the persecuting religion in the wrong, undermining its own legitimacy.
The modern concept of intolerance developed out of the religious controversies between Protestants and Catholics in 17th- and 18th-century England. The doctrine of ‘religious toleration’ at this time, sought to eradicate religious sentiments and dogmas from the political demesne.
The constitutions of some countries contain provisions expressly forbidding the state from engaging in certain acts of religious intolerance or preference within its own borders, examples of such include the First Amendment of the United States Constitution, the Article 4 of the Basic Law of Germany, Article 44.2.1 of the Constitution of The Republic of Ireland, Article 40 of the Estonian Constitution, Article 24 of the Constitution of Turkey, Article 36 of the Constitution of the People's Republic of China, and Article 3 Section 5 of the Constitution of the Philippines.