The Greek Constitution recognizes the Orthodox Christian faith as the "prevailing" faith of the country, while guaranteeing freedom of religious belief for all. The Greek government does not keep statistics on religious groups and censuses do not ask for religious affiliation. According to the U.S. State Department, an estimated 97% of Greek citizens identify themselves as Orthodox Christians, belonging to the Greek Orthodox Church. In a Eurostat – Eurobarometer 2005 poll, 81% of Greek citizens responded that they "believe there is a God", which was the third highest percentage among EU members behind only Malta and Cyprus. According to other sources, 15.8% of Greeks describe themselves as "very religious", which is the highest among all European countries. The survey also found that just 3.5% never attend a church, compared to 4.9% in Poland and 59.1% in the Czech Republic.
Estimates of the recognized Greek Muslim minority, which is mostly located in Thrace, range from 98,000 to 140,000, (between 0.9% and 1.2%) while the immigrant Muslim community numbers between 200,000 and 300,000. Albanian immigrants to Greece are usually associated with the Muslim religion, although most are secular in orientation. Following the 1919–1922 Greco-Turkish War and the 1923 Treaty of Lausanne, Greece and Turkey agreed to a population transfer based on cultural and religious identity. About 500,000 Muslims from Greece, predominantly Turks, but also other Muslims, were exchanged with approximately 1,500,000 Greeks from Asia Minor (now Turkey).
Judaism has existed in Greece for more than 2,000 years. Sephardi Jews used to have a large presence in the city of Thessaloniki (by 1900, some 80,000, or more than half of the population, were Jews), but nowadays the Greek-Jewish community who survived German occupation and the Holocaust, during World War II, is estimated to number around 5,500 people.
Greek members of Roman Catholic faith are estimated at 50,000 with