Croatians are predominately Roman Catholic, a faith which they adopted in the 9th century. The Roman Catholic clergy have played a central role in Croatian education and culture, as well as in preserving Croatian heritage. For example, since the Middle Ages, the clergy promoted the use of Croatian instead of Latin in the Catholic liturgy. Suppressed as a dominant aspect of life under Marshall Tito, Roman Catholicism has become more pronounced since the fall of communism and declaration of independence. When Croatia announced its independence, the Vatican was the first state to officially recognize the republic.

Croatian Roman Catholics are known for their devotion to the Blessed Virgin, known as Gospa. To honour the Queen of Peace, they have built many sanctuaries in various parts of the country, including Marija Bistrica, Trsat, Sinj and Vocin. Pilgrimages to these areas, as well as the celebration of holy days, are a part of spiritual life. The Croatian saints St. Nikola Tavelic, St. Ozona Kotorska and St. Augustus Kazotic date back to the 14th century. St. Leopold Mandic was canonised in 1983 by Pope John Paul II.

Serbian Croatians practise Eastern Orthodox Christianity, which claims to be the oldest or original form of Christianity and which differs from Catholicism in some key areas that have been a source of conflict in Croatia. Whereas Catholics venerate the Virgin Mary and follow the Pope's authority, Eastern Orthodoxy venerates various icons, allows its priests to marry and doesn't recognize the Pope's authority. Protestantism came to Croatia in the 18th century with the migration of Slovaks, Germans and Hungarians. Most Croatian Protestants belong to the Lutheran or Christian Reformed Church.

After Christianity, the two most dominant religions in Croatia are Judaism and Islam. Jews fleeing Byzantium found a safe haven in Croatia in the 8th century and again over the years when their homeland countries expelled or persecuted them. During the Second World War, however, most of Croatia's Jewish population was deported to Nazi concentration camps; other Jews have since emigrated to Israel, leaving the Croatian Jewish population very small. Muslims have lived in Croatia since the 10th century, when they established Turkish settlements. Despite the failed invasions of the Ottoman Empire in the 15th and 16th centuries, relations between Muslim and Christian Croatians have been peaceful.

  Did you know?
On St. John's Day (June 24), some young Croatians celebrate the arrival of the summer solstice by jumping over bonfires.