Most Orthodox Christians celebrated Christmas as believers gathered in Moscow, Kyiv, Bethlehem, Jerusalem, Cairo, and cities throughout the world to mark in the holy day.
Catholics as well Orthodox churches in Romania, Greece, and Bulgaria celebrate Christmas on December 25 under the Gregorian calendar.
The Armenian Orthodox Church celebrated Christmas on January 6.
The January 7 celebrations come amid tensions between the largest Orthodox denomination-- the Russian church-- and the spiritual headquarters for the Orthodox faith in Istanbul.
The Istanbul headquarters, known as the Ecumenical Patriarchate of Constantinople, recently backed an effort by Ukraine to establish its own Orthodox church, independent of Moscow.
Patriarch Bartholomew on January 6 handed over a document known as a "tomos" to the head of the new Ukrainian church, Metropolitan Epifaniy, at a ceremony in Istanbul on January 6.
Hundreds of Ukrainians lined up at Kyiv's St. Sophia Cathedral complex on January 7 to view the document enshrining the newly gained independence of the Orthodox Church in Ukraine.
"For the first time, we celebrate Christmas with an independent autocephalous church," President Petro Poroshenko said after attending services in St. Sophia Cathedral.
"It is the basis of our spiritual freedom, we broke the last fetters tying us to Moscow," he added.
Servicemen of the Interior Ministry of Belarus stand in line to kiss a cross during a service to celebrate Orthodox Christmas at a military base in Minsk on January 7.
Efforts by Ukrainians to establish an independent church intensified after Russia seized Ukraine's Crimean Peninsula in March 2014 and began supporting separatists shortly thereafter in parts of Ukraine's eastern regions of Donetsk and Luhansk.
Orthodox churches, including those in Russia, Ukraine, Georgia, Serbia, and Jerusalem are among Orthodox and Eastern Rite churches that celebrate Christmas observing the old Julian calendar. Currently (1901–2099), the Julian calendar is 13 days behind the Gregorian calendar.
Catholics as well Orthodox churches in Romania, Greece, and Bulgaria celebrate Christmas on December 25 under the Gregorian calendar.
The Armenian Orthodox Church celebrated Christmas on January 6.
In St. Petersburg, Russian President Vladimir Putin on January 7 presented the Transfiguration Cathedral with the icon of Christ Pantocrator as a Christmas gift, while Patriarch Kirill, the head of Russia's Orthodox Church, conducted services in Moscow's Cathedral of Christ the Savior.
Attendance at midnight Christmas Mass has become a tradition for Russian leaders -- some of whom, like longtime KGB officer Putin, were staunch supporters of the communist system during the Soviet era.
Meanwhile, Putin fired a cannon in his native St. Petersburg to mark Christmas. Together with Putin, 85-year-old Vladimir Bendet pulled the lever on the howitzer that fires a daily noontime salute at the Petropavlovsk Fortress on the banks of the Neva River.
In Bethlehem, hundreds of people marked Christmas on January 7 with Greek Orthodox Patriarch Theophilos III at the Church of the Nativity, which was established on ground traditionally recognized as Jesus's birth site.
Palestinian police stood guard as several dozen demonstrators shouted "traitor" in protest of the Greek Orthodox Church's sale of property in mainly Palestinian east Jerusalem to groups promoting Jewish settlements.
Israeli purchases of church land and property in east Jerusalem have angered Palestinians -- including many Orthodox Christians -- who consider the territory to be the capital of their future state. Israel has annexed east Jerusalem, but the move has not been recognized by the international community.
In Cairo, Egypt's president in a symbolic gesture inaugurated a new cathedral for the Coptic Orthodox Church and one of the region's largest mosques. It comes at a time when Islamic militants are increasingly targeting the country's minority Christians in deadly terror attacks.
Abdel Fattah al-Sisi has spoken of sectarian harmony as a major policy goal, but he has still faced criticism for not doing enough to protect Christian and other minorities.
"This is a historic and important moment. But we still have to protect the tree of love we planted here together today because seditions never end," the president said from inside the cathedral.