The Chaldean Catholic Church is an Eastern Syriac particular church of the Catholic Church, under the Holy See of the Catholicos-Patriarch of Babylon, maintaining full communion with the Bishop of Rome and the rest of the Catholic Church.
The Chaldean liturgy can be traced back to the Syriac Christian culture of Edessa, and attained its present basic structure in the 7th century. The liturgical language is Syriac, and a number of Latin customs have been adopted.
A slight reform of the liturgy was effective since 6 January 2007, and it aimed to unify the many different uses of each parish, to remove centuries-old additions that merely imitated the Roman Rite, and for pastoral reasons. The main elements of variations are: the Anaphora said aloud by the priest, the return to the ancient architecture of the churches, the restoration of the ancient use where the bread and wine are readied before a service begins, and the removal from the Creed of the Filioque clause.
The Chaldean Catholic Church presently comprises around 500,000 people.
Most Chaldo-Assyrians live in northern Iraq, with smaller numbers in adjacent areas in northeastern Syria, southeastern Turkey and northwestern Iran.
There are two Chaldean Catholic dioceses in the United States: the Eparchy of St. Thomas the Apostle of the Chaldeans and the Eparchy of St. Peter the Apostle of the Chaldeans in San Diego.
In 2006 a new Eparchy of Saint Thomas the Apostle of Sydney was established for Chaldeans in Australia and New Zealand.
In 2011, Pope Benedict XVI erected a new Chaldean Catholic eparchy in Toronto, Canada.
In other areas of the world, Chaldeans are under spiritual supervision of the local Latin ordinaries.