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.
Theos Kyrios comes after the Great Ektenia (litany) and precedes the apolytikion (troparion of the day), and is chanted in the tone of the week.
The order of Theos Kyrios, as served at Matins is as follows: They then begin immediately to chant the troparia of the day and the corresponding Theotokion.
On days with Allelua, the deacon does not normally serve, so the verses are usually chanted by the priest (according to the Typicon, the canonarch).
They then begin immediately to chant the troparia of the dead: The same format is followed in the Panikhida (requiem service).