Sister Churches, not yet at one altar.

Summary

The Catholic Church teaches that the Orthodox Churches are true particular Churches. The Second Vatican Council says they “possess true sacraments, above all by apostolic succession, the priesthood and the Eucharist, whereby they are linked with us in closest intimacy”⁠.¹ The Congregation for the Doctrine of the Faith adds the reason communion is not full: “they do not accept the Catholic doctrine of the Primacy”⁠.²

Of the differences, one divides: the office of the Bishop of Rome. The Filioque remains a doctrinal question, though Catholic clarifications and joint study have narrowed it⁠.^3,4 Other differences concern doctrine defined in the West: the Immaculate Conception, which the Orthodox reject, and the Assumption and purgatory, which the East approaches through its liturgy and its prayer for the dead rather than through the Latin definitions. Where the two traditions express the same mystery differently, the Council teaches that their theological expressions are “to be considered often as mutually complementary rather than conflicting”⁠.¹ Married priests, leavened bread and the calendar are a legitimate diversity the Council “solemnly declares” the East may keep⁠.¹

On the papacy the official dialogue agrees about the first millennium and not yet about the second. At Ravenna in 2007 both sides agreed that Rome “occupied the first place in the taxis” and that its bishop was “the protos among the patriarchs”⁠.⁵ At Chieti in 2016 they agreed that in the first millennium “the bishop of Rome did not exercise canonical authority over the churches of the East”⁠.⁶ The First Vatican Council defined a “full and supreme power of jurisdiction over the whole church”⁠.⁷ How that definition is to be lived toward Churches that never knew such jurisdiction is the question John Paul II put to all Christians in 1995, when he asked for help “to find a way of exercising the primacy which, while in no way renouncing what is essential to its mission, is nonetheless open to a new situation”⁠.⁸

Restored communion is not near, and the Orthodox world is itself divided: the Russian Orthodox Church broke eucharistic communion with the Ecumenical Patriarchate on Oct. 15, 2018, over Ukraine⁠.⁹ The practical steps continue. In 2025 Leo XIV and Bartholomew I gave thanks that “this year the whole Christian world celebrated Easter on the same day” and set out to seek a common date every year⁠.¹⁰

What the Churches hold in common

The Catholic texts name what the Orthodox Churches have kept, and on these points the two teach the same faith.

The differences, by weight

The differences are not of one kind. One divides the Churches. Some are doctrine the two traditions state differently. The rest is discipline, which the Council treats as the East’s own to keep.

The papacy

The First Vatican Council taught that the Roman pontiff has “the full and supreme power of jurisdiction over the whole church,” not only in faith and morals but in “the discipline and government of the church dispersed throughout the whole world”⁠.⁷ It defined that his ex cathedra definitions are “of themselves, and not by the consent of the church, irreformable”⁠.⁷

The Catholic Church does not treat this as a side issue. The Congregation for the Doctrine of the Faith wrote in 2007 that communion with the Bishop of Rome is “one of its internal constitutive principles” of a particular Church, so the Orthodox Churches “lack something in their condition as particular churches”⁠.²⁴ The same text names the cost on the Catholic side: because of the division, the “fullness of universality” proper to the Church “is not fully realised in history”⁠.²⁴

The joint commission has worked through the history in three documents. Ravenna (2007) agreed that Rome “occupied the first place in the taxis” but recorded: “They disagree, however, on the interpretation of the historical evidence from this era regarding the prerogatives of the bishop of Rome”⁠.⁵ It left the rest for later: “It remains for the question of the role of the bishop of Rome in the communion of all the Churches to be studied in greater depth”⁠.⁵ Chieti (2016) agreed on the first millennium⁠,⁶ with the Georgian delegation recording disagreement with some paragraphs⁠.²⁵ Alexandria (2023) took up the second millennium and concluded that the Church “is not properly understood as a pyramid, with a primate governing from the top, but neither is it properly understood as a federation of self-sufficient Churches”⁠.¹⁸

Joseph Ratzinger, as a theologian, gave the formula most often cited on the Catholic side: “Rome must not require more from the East with respect to the doctrine of primacy than had been formulated and was lived in the first millennium”⁠.²⁶ John Paul II opened the question to all Christians in Ut Unum Sint⁠,⁸ and in 2024 the Dicastery for Promoting Christian Unity published The Bishop of Rome, the first synthesis of the responses to that invitation⁠.²⁷

The Filioque

The Creed of 381 says the Holy Spirit proceeds from the Father. The words “and the Son” were “inserted into the Latin Creed by Pope Benedict VIII in 1014”⁠.¹⁴ The Council of Florence defined that the Spirit “is eternally from the Father and the Son” and recorded that the Greek fathers who said “from the Father through the Son” were “aiming at the same meaning in different words”⁠.¹³

In 1995 the Pontifical Council for Promoting Christian Unity published the clarification John Paul II had asked for, to show the Latin formula’s “full harmony” with Constantinople, which confesses “the Father as the source of the whole Trinity, the one origin both of the Son and of the Holy Spirit”⁠.³ It affirms that the Spirit takes his origin from the Father “in a principal, proper and immediate manner”⁠.³ In North America, Catholic and Orthodox theologians went further in 2003 and recommended “that the Catholic Church, as a consequence of the normative and irrevocable dogmatic value of the Creed of 381, use the original Greek text alone in making translations of that Creed for catechetical and liturgical use”⁠.⁴

Mary, purgatory and the theology of grace

The Council’s principle for these questions is in the Decree on Ecumenism: one tradition has sometimes “come nearer to a full appreciation of some aspects of a mystery of revelation than the other,” and the two expressions are “often as mutually complementary rather than conflicting”⁠.¹

Pius IX defined in 1854 that Mary was “preserved free from all stain of original sin”⁠,¹⁵ and Pius XII in 1950 that she “was assumed body and soul into heavenly glory”⁠.¹⁷ The Christians of the East “pay high tribute, in beautiful hymns of praise” to the Mother of God⁠,¹ and Pius XII drew on the liturgical books for “the feast either of the dormition or of the Assumption” as witnesses to the dogma⁠.¹⁷ The Orthodox Church in America gives the Orthodox reason in its life of the feast of the Conception of the Theotokos: “The Orthodox Church does not accept the teaching that the Mother of God was exempted from the consequences of ancestral sin (death, corruption, sin, etc.) at the moment of her conception by virtue of the future merits of her Son”⁠.¹⁶

On the state of the dead, both Churches pray for the departed. Florence defined “the pains of purgatory” and the value of “suffrages offered for the dead”⁠.¹³ The joint commission’s Alexandria document counts purgatory among the “disputed points” in the profession accepted at Lyon in 1274, which “was rejected by the Church of Constantinople in 1285”⁠.¹⁸

Sharing the sacraments

Because the Orthodox sacraments are true sacraments, the Council judged that “some worship in common ( communicatio in sacris ), given suitable circumstances and the approval of Church authority, is not only possible but to be encouraged”⁠.¹ Canon law lets a Catholic minister give penance, the Eucharist and the anointing of the sick to Orthodox faithful who “seek such on their own accord and are properly disposed”⁠.¹¹ The canon binds Catholic ministers only; the Orthodox Churches set their own discipline.

The Holy and Great Council held in Crete in 2016 “accepts the historical name of other non-Orthodox Christian Churches and Confessions” while holding that its own unity “can never be perturbed”⁠.²⁸ Each side calls the other a Church, and each means something different by it.

From 1014 to 2025

Nicaea, 1,700 years on

On Nov. 28, 2025, at the invitation of Patriarch Bartholomew, Pope Leo XIV prayed with him and with representatives of other Churches at İznik, the ancient Nicaea, by the excavations of the Basilica of St. Neophytos⁠.³² He thanked Bartholomew for marking the 1,700th anniversary of the Council in the place where it was held, and said that “we must strongly reject the use of religion for justifying war, violence, or any form of fundamentalism or fanaticism”⁠.³³ Bartholomew said, “We return to this wellspring of the Christian faith in order to move forward”⁠.³⁴ The next day they signed the joint declaration quoted above⁠.¹⁰

Moscow, Constantinople and Ukraine

Moscow and Constantinople have been out of communion since 2018 over Ukraine, and Moscow has refused communion with any primate who recognizes the Orthodox Church of Ukraine⁠.³⁵ After Constantinople named two exarchs to Kyiv, the Holy Synod of the Moscow Patriarchate on Sept. 14, 2018, suspended the commemoration of Patriarch Bartholomew and concelebration with his hierarchs, and broke off its part in the episcopal assemblies, theological dialogues and commissions chaired or co-chaired by Constantinople⁠.³⁶ On Oct. 11 the Holy Synod of the Ecumenical Patriarchate renewed its decision to grant autocephaly to the Church of Ukraine, re-established its stavropegion in Kyiv, received Filaret Denisenko and Makariy Maletych into communion, and lifted the force of the 1686 synodal letter, which in its reading had granted the Patriarch of Moscow only the right to ordain the Metropolitan of Kyiv⁠.³⁷ Meeting in Minsk on Oct. 15, Moscow’s synod declared continued eucharistic communion with Constantinople impossible until it renounced what the synod called its anti-canonical decisions⁠.³⁸

The tomos, dated Jan. 6, 2019, declared autocephalous the Orthodox Church within the borders of the Ukrainian state, to be called the Most Holy Church of Ukraine, with its jurisdiction limited to that state’s territory, and was handed to its primate, Metropolitan Epiphanius⁠.³⁹ It says that Ukraine’s civil and church leaders had sought autocephaly for 30 years and that Constantinople acted to heal long-standing schisms⁠.³⁹

The break reached the dialogue with Rome. Meeting Pope Francis on Oct. 19, 2018, Metropolitan Hilarion of Volokolamsk, chairman of the Moscow Patriarchate’s Department for External Church Relations, said the Russian Church was obliged to suspend its part in the Joint International Commission for Theological Dialogue, while its relations with the Catholic Church would continue to develop⁠.⁴⁰ The commission’s coordinating committee, co-chaired by Cardinal Kurt Koch and Metropolitan Job of Pisidia of the Ecumenical Patriarchate, met in Rethymno, Crete, in September 2025 and took up a draft text on infallibility⁠.⁴¹

Each side states its case. Moscow’s bishops wrote in 2023, “The direct cause of the crisis was the incursion of the Patriarchate of Constantinople into Ukraine”⁠.³⁵ Patriarch Bartholomew rejected in 2024 the idea of a “Third Rome” and called the ideology of the “Russian World” the main instrument for a spiritual legitimation of the invasion of Ukraine⁠.⁴²

Inside Ukraine, the council of the Ukrainian Orthodox Church condemned the war on May 27, 2022, voiced its disagreement with Patriarch Kirill’s position on it, and adopted statute amendments that it said attest to its full independence⁠;⁴³ Moscow’s synod answered that a change in that Church’s status could be made only through a canonical procedure that includes a decision of the Local Council of the Russian Orthodox Church⁠.⁴⁴ Law No. 3894-IX, adopted by the Verkhovna Rada on Aug. 20, 2024, and in force since Sept. 23, 2024, prohibits the activity of the Russian Orthodox Church in Ukraine and provides for religious organizations affiliated with it to be terminated in the manner the law sets out, citing that Church’s support for Russia’s aggression⁠.⁴⁵ Major Archbishop Sviatoslav of the Ukrainian Greek Catholic Church said the law was not a ban on the Church but a protection against the use of religion as a weapon, and urged attention to how it is applied⁠.⁴⁶ The Moscow Patriarchate called the law a “clear violation of internationally recognised human rights in the field of religious freedom”⁠.⁴⁷ In 2025 the state’s religious affairs service found that the Ukrainian Orthodox Church, through its Kyiv Metropolis, retains signs of subordination to the Russian Church, and the Metropolis said it could not comply with the order⁠.⁴⁸

Popes have spoken with the Moscow Patriarchate directly. In a video call on March 16, 2022, Pope Francis told Patriarch Kirill that the Church “must not use the language of politics, but the language of Jesus”⁠.⁴⁹ A second meeting planned for Jerusalem that June was called off⁠.⁵⁰ Recounting the call in a Corriere della Sera interview published May 3, 2022, he said, as Vatican News reported, “Il Patriarca non può trasformarsi nel chierichetto di Putin” (the Patriarch cannot turn himself into Putin’s altar boy)⁠;⁵¹ the Department for External Church Relations answered that the Pope had chosen an incorrect tone and that such statements were unlikely to help constructive dialogue⁠.⁵² Of “the laws recently adopted in Ukraine,” Francis said on Aug. 25, 2024, “If someone commits evil against his people, he will be guilty for that, but he cannot have committed evil because he prayed,” and asked that “no Christian Church be abolished directly or indirectly”⁠.⁵³

Contacts have continued under Pope Leo XIV. He received Metropolitan Anthony of Volokolamsk, chairman of the Department for External Church Relations, in private audience on July 26, 2025⁠;⁵⁴ by the Department’s account, the Metropolitan “informed Pope Leo XIV about the persecution currently faced by the Ukrainian Orthodox Church”⁠.⁵⁵ In Moscow on Aug. 25, 2026, Archbishop Paul Richard Gallagher, the Holy See’s secretary for relations with states and international organizations, told reporters after meeting Foreign Minister Sergey Lavrov that “this war must end,” and met Metropolitan Anthony that evening⁠.⁵⁶

What would move it

• A common account of the primacy. Ravenna, Chieti and Alexandria have prepared the ground, and the next step is the one Ravenna named: the role of the bishop of Rome “to be studied in greater depth”⁠.⁵
• A common Easter. The 2025 declaration speaks of “exploring a possible solution for celebrating together the Feast of Feasts every year”⁠.¹⁰
• Peace between Greek Catholics and Orthodox. Havana says the Eastern Catholic communities “have the right to exist” and that the past method of uniatism “is not the way” to restore it⁠.²³
• Healing among the Orthodox themselves, since Moscow and Constantinople are not in communion with each other⁠.⁹

The Catholic Church asks of her own members first that they know the Eastern tradition, “so as to be nourished by it”⁠.¹² The rest is the work of the bishops, and of prayer.