The Metropolis of Chalcedon (Greek: Μητρόπολη Χαλκηδόνος) is an ecclesiastical territory (diocese) of the Ecumenical Patriarchate of Constantinople. The metropolis is led by Metropolitan Emmanuel (Adamakis) since 2021.

Christianity spread in Chalcedon during the 2nd century AD. The city was initially the see of a bishopric before being promoted to a metropolis at 451 AD, at the time of the Fourth Ecumenical Council. In 2005, it was the senior of the four remaining active Greek Orthodox Church metropolises of the Ecumenical Patriarchate in Turkey and the only one surviving in Asia Minor (Anatolia). As of 2024, it is numbered as the senior of nine active Metropolises that are active in Turkey, after the Archdiocese of Constantinople-New Rome.

Christianity spread in the region of Chalcedon, on the Asian shore opposite Byzantium (later Constantinople) already from the 2nd century AD. Among the first bishops, Hadrian was martyred during the 2nd (or 4th) century and is venerated by the Orthodox Church. Chalcedon was also the place of martyrdom of saint Euphemia.

The city of Chalcedon enjoyed considerable prestige thanks to the Ecumenical Council that was convoked there at 451 AD, after the initiative of Byzantine Emperor Marcian and Empress Pulcheria. Its aim was to denounce the decisions of the Second Council of Ephesus, commonly known as the Robber Council, in 449. The decisions of the Council consolidated the Nicene Creed and renounced as heretical number of contemporary doctrines: Apollinarism, Monophysitism and Nestorianism. On the other hand, Jesus Christ was accepted as perfect God and human with logical soul. Moreover, it recognized two indivisible and inseparable natures in Jesus. It also accepted the nature of Virgin Mary as Mother of God (Theotokos). According to the 28th canon of the Council, the Church of Constantinople gained privileges equal to those of Rome, which however were not clearly defined. The same canon clarified that the bishop of Constantinople held the prerogative of honors right after the bishop of Rome.

In 451, the year that the local Ecumenical Council took place, the bishopric of Chalcedon was promoted to a metropolis. It was the third oldest metropolis in the region of Bithynia, in northwestern Asia Minor, after Nicaea and Nicomedia, while its prelate officially styled as Exarch of all Bithynia.

A number of metropolitans and bishops of Chalcedon participated in the Byzantine Iconoclasm dispute, during the 8th–9th centuries. Some of them were martyred and are venerated by the Orthodox Church, like Metropolitans Nicetas, Kosmas and John. In 858 the local metropolitan, Basil, due to his participation in the Photian schism, was released from his duties by Patriarch Photios. However, later, in 869–870, after the restoration of patriarch Ignatios, Basil returned to the metropolitan throne where he remained until 877.

Later, ca. 1100, Metropolitan Leo was involved in ecclesiastical issues and was accused of heresy. He also accused Emperor Alexios I Komnenos of sacrilege and iconoclasm, because he allowed the melting of religious gold and silver objects in order to sustain his war effort.

Due to the long tradition of Saint Euphemia and its association with the area of Chalcedon, the local metropolitans claimed and occasionally succeeded in controlling a number of churches and shrines dedicated to her in the region of Constantinople.