Theos Kyrios (Greek: Θεὸς Κύριος, "God is the Lord", or "The Lord is God") is a psalm response chanted near the beginning of the Matins service in the Rite of Constantinople, observed by the Eastern Orthodox and Byzantine Catholic churches. It is based principally on Psalm 117 (Septuagint numbering), the refrain composed of verses v. 27a and 26a.