But in Russia, Serbia, Ukraine and other Orthodox countries that observe a different religious calendar, it is Christmas Eve. Roman Catholics and Protestants, meanwhile, celebrate the story of the Wise Men who followed a star to Jesus' cradle.
Here's a look at celebrations taking place on Wednesday:
GREECE
Ceremonies were held across the country, with divers jumping from piers, bridges and tug boats. School children and members of the country's navy special forces also took part.
The main ceremony was held at the country's largest port of Piraeus, near Athens, but left-wing Prime Minister Alexis Tsipras attended a smaller ceremony in the Greek capital following a spat with traditionalists in the Orthodox Church who vehemently opposed a recent law sanctioning same sex-civil partnerships.
Bishop Serapheim of Piraeus described the law an "insult to human identity" and "psychiatric deviation from healthy sexuality."
CYPRUS
More than 1,000 Orthodox Christian faithful attended the annual Epiphany Day blessing of the waters in Famagusta in Cyprus' breakaway Turkish Cypriot north. It was the first time the ceremony has taken place since 1974 when Turkey invaded after a coup aiming at union with Greece divided the island.
In keeping with tradition, Archimandrite Avgoustinos Karras hurled a silver cross into the cold waters of the eastern Mediterranean as about 20 daring swimmers dashed into the sea to retrieve it. The ritual is called the Blessing of the Water and symbolizes Jesus' baptism in River Jordan.
Organizer Pavlos Iacovou told The Associated Press that several Turkish Cypriots also attended Wednesday's ceremony.
Acting as the backdrop to the ceremony was the Turkish military-controlled suburb of Varosha that has remained a virtual ghost town for 42 years, ensconced in a chain-link fence that keeps everyone out.
The ceremony was the latest in a number of recent, faith-oriented acts of rapprochement between the island's majority Orthodox Christian, Greek-speaking and the Muslim, Turkish speaking populations. They aim to underscore that religion doesn't drive a wedge between Greek and Turkish Cypriots.
VATICAN
Pope Francis says restless hearts these days are seeking sure answers to life's questions but don't find them.
Francis has voiced this reflection during Mass in St. Peter's Basilica Wednesday to mark Epiphany, which recalls the Gospel account of the Three Kings, or Magi, who followed a star to find baby Jesus in Bethlehem.
The pontiff said: "Like the Magi, countless people in our day have a 'restless heart' which continues to search without finding sure answers."
TURKEY
Members of Istanbul's tiny Greek Orthodox community, visitors from neighboring Greece and other faithful attended an Epiphany service led by Ecumenical Patriarch Bartholomew I, the spiritual leader of the world's Orthodox Christians in Istanbul, where the Patriarchate is based.
A group of faithful leaped into the frigid waters of the Golden Horn inlet to retrieve a wooden cross thrown by Bartholomew. Nicolaos Silos, a 28-year-old visitor from Greece, was the first to reach it.
A ceremony to bless the waters was also held in Izmir, Turkey's third-largest city. It was the first "official" Epiphany ceremony there since the end of a Greek-Turkey war nearly a century ago that triggered a population exchange between Greece and Turkey. Although the Greek Consulate in Izmir had organized a ceremony 2006, it was the first time the Turkish government both approved and helped to organize it.
"It's a historic day here and we're grateful to the local authorities and to the Patriarchate ... for making this happen," Tina Samoglu, secretary of the Izmir Orthodox Community told Greek state TV. "I feel very proud and I'm filled with emotion."
The patriarchate in Istanbul dates from the 1,100-year-old Orthodox Greek Byzantine Empire, which collapsed when the Muslim Ottoman Turks conquered Constantinople, today's Istanbul, in 1453.
RUSSIA
Russian President Vladimir Putin attended midnight Mass in a church in the village of Turginovo, about 150 kilometers (90 miles) northwest of Moscow. Russian news reports said the church was where his parents had been baptized. Putin stood in a black jacket and an open-collar shirt with several solemn-faced children standing around him.
The head of the Russian Orthodox Church, Patriarch Kirlill, led the night Mass at Moscow's sprawling Christ the Savior Cathedral, a service broadcast live on state television. Prime Minister Dmitry Medvedev was among the throng in the cathedral, which was destroyed under Soviet dictator Josef Stalin then reconstructed after the fall of Communist rule.
It will also be the first time since 1928 that a Christmas Eve Mass has been held in the world's largest Orthodox basilica, the St. Isaac's Cathedral in St. Petersburg.
The landmark 19th Century cathedral was turned into a museum under the officially atheist Soviet regime; after the USSR's collapse in 1991 it remained as a museum, but the Russian Orthodox church has used it periodically for services.
BULGARIA
Thousands of young men waded into icy waters in Bulgaria to retrieve crucifixes cast on the waters by priests. By tradition, the person who retrieves it will be healthy and freed from evil spirits all year. After the cross is fished out, the priest takes a bunch of dried basil to sprinkle water over believers.
In some villages, men dipped into a local river and danced the horo, a traditional dance. In the mountain village of Kalofer, in central Bulgaria, scores of men in traditional dress waded into the icy Tundzha River carrying national flags.
Led by a drummer and several men playing the bagpipes, they danced in the freezing waters, pushing away floating chunks of ice. Some sipped plum brandy and red wine as an antidote to the freezing weather.
SPAIN
Children across Spain woke up Wednesday to open presents left during a night-time "visit" by the Three Kings of Orient, a tradition similar to that of Santa Claus but celebrated annually on Epiphany.
Expectations were raised the previous evening as towns and cities across the country held Epiphany parades or cavalcades symbolizing the coming of the Magi to Bethlehem laden with gifts for the baby Jesus.
Thousands of children and parents thronged sidewalks in Madrid and other cities to watch as ornately decorated floats — including in some cases men dressed as kings riding camels or horses — were accompanied by clowns, jugglers and marching bands.
The tradition spread from Spain to many Latin American countries where Epiphany is the day when gifts are exchanged.
WEST BANK
The Greek Orthodox Patriarch of the Holy Land, Theofilos III, arrived in Bethlehem on Wednesday for Orthodox Christmas celebrations.
But he received a cool reception. A scout troop that traditionally greets the patriarch didn't show up, and few followers joined him in his traditional procession to the Church of Nativity.
Many Palestinians are angry at the patriarch, accusing him of selling land to Israel and to private investors, punishing popular clergymen and being secretive with church funds.
UKRAINE
Rebels in the east said they were willing to release captives taken during the conflict to mark Christmas. It was unclear however, if Ukrainian authorities would be willing to do a prisoner exchange.
The rebels in Donetsk said they wouldn't engage in a release without a similar release by Kiev. But Igor Plotnitsky, leader of rebels in Luhansk, said his forces were prepared for a release without any reciprocal move by Kiev.
It was not known how many prisoners each sides are holding or how many might be eligible for the potential release. As of early Thursday, there were no reports that either side had freed any captives.
ROMANIA
Hundreds of Romanian villagers gathered on the fields near the southern village of Pietrosani, where a priest blessed horses in a traditional Epiphany ritual to ward off diseases and bad luck during the year.
Orthodox priests sprinkled holy water on more than a dozen horses, which were decorated with red tassels, ear caps and ankle bands for good luck. The animals are essential to village life, and are used for plowing, carrying wood and transport.
Horses, ridden bareback, later thundered across the icy fields in the annual race. Villagers drank plum brandy and mulled wine and ate grilled spicy sausages to celebrate the feast while horses dragged logs to demonstrate their strength.
MEXICO
Several thousand people gathered in Mexico City's huge Zocalo plaza on Tuesday evening to partake in a gigantic Three Kings Day cake known as a "rosca."
The pastry weighed 9.3 metric tons and formed a loop that was 1,440 meters long.
Mexico City's local government sponsored the free event, which is held annually, and Mayor Miguel Angel Mancera was on hand to cut the cake.
The Three Kings are beloved in Mexico, as in other parts of Latin America, by children who wait for the wise men to bring them gifts on Epiphany eve.
UNITED STATES
In New Orleans, Carnival season begins on Jan. 6 — the "Twelfth Night" after Christmas. The Carnival season is celebrated along the Gulf Coast with parties, balls and parades culminating on Mardi Gras, or Fat Tuesday, a final day of celebration before the solemnity of Ash Wednesday and Lent. Mardi Gras falls on Feb. 9 this year. The countdown to Mardi Gras is marked by a streetcar full of raucous costumed revelers. The group known as the Phunny Phorty Phellows kicks off Carnival season Wednesday night by riding a streetcar through the city along famed St. Charles Avenue. And bakeries across the city have started churning out king cakes — an oval-shaped pastry with a plastic doll hidden inside. Whoever finds the doll is dubbed "king" and buys the next cake.
PUERTO RICO
In the U.S. territory of Puerto Rico, a worsening economic crisis has for the first time dampened a popular government-sponsored celebration of Three Kings Day that typically draws thousands of families.
The Puerto Rican government, which was criticized in 2011 for giving out laptops to children amid an economic crisis, announced this week that it would greatly scale back this year's celebration and would only hand out a limited number of balls to children.
Officials also moved the territory's annual celebration to the central mountain town of Utuado, which agreed to pick up part of the bill because of the central government's dwindling cash flow.
In previous years, families formed long lines overnight in the capital of San Juan to receive gifts from the government.
CZECH REPUBLIC
Epiphany is linked to a major charity event, which some 60,000 to 70,000 volunteers all across the country take to the streets to collect money to help people in need at home and abroad.
Last year, they collected about 90 million koruna ($3.6 million). The collection is organized by the Caritas Czech Republic, a charity organization of the Roman Catholic Church. Ten percent is designed for aid abroad.
In Prague, the capital of the Czech Republic, dozens of polar swimmers braved heavy snowing and freezing temperatures to take part Wednesday in the traditional Epiphany swim in the Vltava River near the famed Charles Bridge.
POLAND
President Andrzej Duda, the first lady and hundreds of residents walked in a cheerful Epiphany procession in sub-freezing temperatures in downtown Warsaw.
The procession was led by Cardinal Kazimierz Nycz, the archbishop of Warsaw, and by colorfully dressed actors in the roles of the Three Magi, riding on a camel, a horse and a paper dragon. It ended with the crowd singing carols in the central Pilsudski Square.
Similar processions were held in other cities across the predominantly Catholic Poland, which will be marking 1050 years of Christianity in April.
EGYPT
Egyptian Copts are expected to flock to Cairo's Orthodox Cathedral to attend Christmas services on Wednesday amid tightened security ahead of the 2011 uprising's anniversary. Fears of potential attempts to mark the anniversary of the revolt with protests have been on the rise in recent weeks.
Egypt's Orthodox Coptic Christians make up about 10 percent of the country's 90 million people. The Copts have long complained of discrimination and largely supported the military's overthrow of the first freely elected, but divisive Islamist President Mohammed Morsi in 2013. Ever since, Christian gatherings are believed to be at an even greater risk of militant attacks.
(AP)
An Albanian man hands over to the priest the cross he retrieved from the
Osum River in the southern city of Berat, Albania thrown there by an
Eastern Orthodox priest to celebrate Epiphany day as people believe that
the one who retrieves it will be healthy through the year, Wednesday,
Jan. 6, 2016. Albania is known for its religious coexistence where the
Orthodox and Catholic communities live in peace with the majority
Muslims.
An Albanian man hands over to the priest the cross he retrieved from the
Osum River in the southern city of Berat, Albania thrown there from an
Eastern Orthodox priest to celebrate Epiphany day as people believe that
the one who retrieves it will be healthy through the year, Wednesday,
Jan. 6, 2016. Albania known for its religious coexistence where the
Orthodox and Catholic communities live in peace with the majority
Muslims.
Spain's King Felipe VI and his wife Queen Letizia shake hands welcoming
their guests during the annual Pascua Militar Epiphany ceremony at the
Royal Palace in Madrid, Spain, Wednesday, Jan. 6, 2016.
Citizens of Warsaw participate at the Epiphany parade in Warsaw,
Poland, Wednesday, Jan. 6, 2016. The Epiphany day celebrates the visit
of the Three Kings to the infant Jesus.
A woman kisses a candle before joining Ecumenical Patriarch Bartholomew
I, the spiritual leader of the world's Orthodox Christians, for an
Epiphany ceremony at the Patriarchate in Istanbul, Wednesday, Jan. 6,
2016. The traditional Epiphany ceremony marks the Epithany in Istanbul
when Bartholomew I or an Orthodox priest throws a simple wooden cross
into the water to bless the water at the Golden Horn and swimmers race
to be the first to retrieve it.
A woman lights a candle before joining Ecumenical Patriarch Bartholomew
I, the spiritual leader of the world's Orthodox Christians, for an
Epiphany ceremony at the Patriarchate in Istanbul, Wednesday, Jan. 6,
2016. The traditional Epiphany ceremony marks the Epithany in Istanbul
when Bartholomew I or an Orthodox priest throws a simple wooden cross
into the water to bless the water at the Golden Horn and swimmers race
to be the first to retrieve it.
Citizens of Warsaw watchingthe Epiphany parade in Warsaw, Poland,
Wednesday, Jan. 6, 2016. The Epiphany day celebrates the visit of the
Three Kings to the infant Jesus.
Citizens of Warsaw watching the Epiphany parade in Warsaw, Poland,
Wednesday, Jan. 6, 2016. The Epiphany day celebrates the visit of the
Three Kings to the infant Jesus.
A horse tries to remove the blanket that covers it before a traditional
Epiphany celebration horse race in Pietrosani, Romania, Wednesday, Jan.
6, 2016. According to the local Epiphany traditions, following a
religious service villagers get their horses blessed with Holy water
then compete in a race.
Villagers compete during a traditional Epiphany celebration horse race
in Pietrosani, Romania, Wednesday, Jan. 6, 2016. According to the local
Epiphany traditions, following a religious service villagers get their
horses blessed with Holy water then compete in a race.
Bosnian Serb men warming themselves near a fire as they prepare to roast
a pig, a traditional meal for Orthodox Christmas, in Bosnian town of
Pale, near Sarajevo, Bosnia, Wednesday, Jan. 6, 2016. Bosnian Serbs, as
Orthodox Christians, celebrate Christmas on Jan. 7, where they use the
Julian calendar instead of the 16th-century Gregorian calendar adopted
by Catholics and Protestants and commonly used in secular life around
the world.
Actors dressed in a Santa Claus costumes walk past a kiosk selling
T-shirts with a portrait of the Russian President Vladimir Putin during
celebrations of the upcoming Orthodox Christmas at a Christmas market in
St.Petersburg, Russia, Wednesday, Jan. 6, 2016. The sign on the T-shirt
signs 'The most polite man'.
An actors dressed as Grandfather Frost, Russian Santa Claus, rides past a
kiosk selling T-shirts with a portrait of the Russian President
Vladimir Putin during celebrations for the upcoming Orthodox Christmas
at a Christmas market in St.Petersburg, Russia, Wednesday, Jan. 6, 2016.
The sign on the T-shirt signs 'The most polite man'.