Relations have been tense for nearly 1,000 years between the Eastern and Western branches of Christianity since the Great Schism of 1054.
For centuries ecclesiastical and political differences bred distrust, with the Orthodox Church accusing the Vatican of trying to convert Russians following the fall of the Soviet Union. The Vatican has always denied such allegations.
One of the most significant disputes, is over the fate of many church properties that Soviet leader Joseph Stalin confiscated from Eastern Rite Catholics, who worship in an Orthodox rite but owe their allegiance to Rome.
Stalin gave the property to the Russian Orthodox Church but after the fall of communism, the Eastern Rite Catholics took back more than 500 churches, mostly in Western Ukraine.
However, since Pope Benedict XVI succeeded in 2005, there have been signs from both sides of a détente.
In 2009, the Vatican and Russia established full diplomatic ties, after the then President Medvedev visited the Pope in the Vatican.
And in 2011, in an interview with Reuters, a senior Bishop of the Russian Orthodox Church, Archbishop Hilarion, urged the Vatican to show further signs of readiness to resolve their differences.
He suggested that an unprecedented meeting between the Pope and Patriarch Kirill of the Orthodox Church would help to unify Christians around the world.
Hilarion said Benedict XVI helped to improve relations and showed "more sensitivity to the Orthodox tradition than his predecessor.”
Pope John Paul’s fight against communism in Poland was seen by some in the Orthodox Church as a crusade against Russia.
And now with Pope Benedict XVI’s resignation, negotiations between the Catholic and Orthodox Churches, may have hit another bump in the road.
His successor will take on the difficulties of the entrenched strong feelings on both sides, if a historic meeting between the leaders of both churches can be achieved.
Vatican spokesman Federico Lombardi said: "The pope announced that he will leave his ministry at 8:00pm (7pm UK time) on February 28."
This is the full speech from the Vatican radio station:
I have convoked you to this Consistory, not only for the three canonisations, but also to communicate to you a decision of great importance for the life of the Church. After having repeatedly examined my conscience before God, I have come to the certainty that my strengths, due to an advanced age, are no longer suited to an adequate exercise of the Petrine ministry.
I am well aware that this ministry, due to its essential spiritual nature, must be carried out not only with words and deeds, but no less with prayer and suffering. However, in today’s world, subject to so many rapid changes and shaken by questions of deep relevance for the life of faith, in order to govern the bark of Saint Peter and proclaim the Gospel, both strength of mind and body are necessary, strength which in the last few months, has deteriorated in me to the extent that I have had to recognise my incapacity to adequately fulfil the ministry entrusted to me.
For this reason, and well aware of the seriousness of this act, with full freedom I declare that I renounce the ministry of Bishop of Rome, Successor of Saint Peter, entrusted to me by the Cardinals on 19 April 2005, in such a way, that as from 28 February 2013, at 20:00 hours, the See of Rome, the See of Saint Peter, will be vacant and a Conclave to elect the new Supreme Pontiff will have to be convoked by those whose competence it is.
Dear Brothers, I thank you most sincerely for all the love and work with which you have supported me in my ministry and I ask pardon for all my defects. And now, let us entrust the Holy Church to the care of Our Supreme Pastor, Our Lord Jesus Christ, and implore his holy Mother Mary, so that she may assist the Cardinal Fathers with her maternal solicitude, in electing a new Supreme Pontiff. With regard to myself, I wish to also devotedly serve the Holy Church of God in the future through a life dedicated to prayer."
From the Vatican, 10 February 2013
BENEDICTUS PP XVI