The Tevinter Chantry is the dominant religious organization in the Empire of Tevinter, and while continent wide diminitive it is large in Thedas and the major order of the Chantry. It is based on the Chant of Light, a series of teachings written by Andraste, the prophet of the Maker, and was founded by Kordillus Drakon, the first emperor of Tevinter, and has since its early days split further and further from the main Andraste Chantry.
The Chantry's followers are known as Andrastians. "Chantric" is also an acceptable adjective to refer to something or someone that is of the Chantry religion.
The Imperial Chantry does not recognize the Divine of the Chantry of Andraste in Orlais, but elects its own Imperial Divine—sometimes called the "Black Divine" by the Chantry of Andraste. This "Black Divine" is known to reside in the Argent Spire in Minrathous, therefore it can be assumed that this is where the Imperial Chantry's headquarters are located. In contrast to the Andrastian Chantry, the Imperial Chantry allows male priests and has more tolerant views of mages and magic.
The principal teaching of the Tevinter Chantry (and the one which led to the schism with the Andraste Chantry), is their interpretation of the words, "magi exists to serve man, and never to rule over him." The magisters interpret this to mean that magic must serve the greater good, which they claim to be accomplished through Magi rule. The Tevinter priests altered the Chant to reflect that magic must be used in the service of all mankind for their prosperity and condemned the Chantry in Orlais. This allowed the magisters to reclaim their ancient authority and once again rule the Imperium. Meanwhile, the Chantry in Orlais remains firm in its belief that Magi are untrustworthy and should be controlled. Both Chantries condemn each other about their views on magic.
When Emperor Kordillus Drakon decreed Divine Justinia I head of the Andrastian Chantry, it upset the Tevinters, who had already organized their own Chantry with the Archon serving as its head before Orlais was ever unified, believing their country to be the Holy Land, as Andraste had lived and died there.