The kliros (Greek: κλήρος, plural κλήροι, "kliroi"; Slavonic: клиросъ, "kliros" or sometimes крилосъ, "krilos") is the section of the church dedicated to the choir. It refers both to the general space in which chanters or singers assemble for the services, as well as to the actual musical stand or shelves on which music is stored and read.
Historically, in cathedrals, monasteries and larger establishments such as chapels belonging to seminaries and major parishes, there would have been kliroses on both right and left sides of the church. The result is two choirs which sing antiphonally, much as monastic and cathedral choirs of the Western Churches still have today. This was the practice in the Byzantine Imperial Cathedral of Hagia Sophia, in Constantinople, whose historical liturgical practice became the standard for all churches following the Byzantine typikon.
This arrangement presupposes a number of singers on each side, adding up to a reasonably large total, and two highly-trained chanters skilled in leading the services. Unfortunately, highly-trained chanters are exceedingly rare today, and most churches have only the one kliros, often to the right of the iconostasis. Nevertheless some patriarchal cathedrals, larger monastic communities, seminaries, and places with sufficient resources and singers, may continue to have two kliroses.
Orthodox parishes that use buildings previously owned or built by other Christian traditions, will sometimes use the choirloft above the great doors of the east end as a kliros.
In churches of the Greek and some parts of the Russian tradition, chanters and men who sing at the kliros will often wear outer-cassocks. In the Armenian tradition, both men and women of the choir at the kliros will wear sticharia.