The eastern Orthodox church has over 250 million members around the world.
Its spiritual leader is based in Istanbul.
But for followers in Ukraine, there's a new found independence.
Churches there have officially cut ties with their Russian branch - accusing it of what they call 'pro-Moscow propaganda'.
The decision has angered Russian leaders, with Moscow warning of what it calls dire consequences.
So, was this a politically motivated decision?
Valentin Yakushik - Professor of Political Science at the National University of Kyiv-Mohyla Academy.
Marat Shterin - Professor of Sociology of Religion and Department Head of Theology and Religious Studies at King’s College London.
Alexander Bratersky - Senior Foreign Policy at Gazeta.ru newspaper.
Check our website: http://www.aljazeera.com/