Roman Catholicism is the major religion of Italy. There are mature Protestant and Jewish communities and a growing Muslim community, the latter made up primarily of new immigrants. All religious faiths are provided equal freedom by the constitution. Before the adoption of Christianity as the official religion of the state, in the fourth century, the country was officially pagan and worshipped the Roman gods, although there was great religious tolerance. As Edward Gibbon said in his The Decline and Fall of the Roman Empire, "The various modes of worship which prevailed in the Roman world were all considered by the people as equally true; by the philosopher as equally false; and by the magistrate as equally useful."

The adoption of Christianity by Constantine in the fourth century led to its becoming the majority religion of the Roman Empire and Italy. The head of the Roman Catholic church, the bishop of Rome, known as the pope, resides in Vatican City, in Rome but not a part of Rome.

Islam, though historically present in Sicily during the Arab occupation in the Middle Ages, was almost entirely absent in Italy from the time of that country's unification in 1861, until the 1970s, when the first North African immigrants began to arrive. These North Africans, mostly of Berber or Arab origin, came mainly from heavily Islamic Morocco, though they have been followed in more recent years by Tunisians, Albaniansand to a lesser extent, Libyans, Egyptians, Pakistanis, Middle Eastern Arabs, and Kurds.