The Polychronion is a solemn encomium chanted in the liturgy of the Eastern Orthodox Church and those Eastern Catholic Churches which follow the Byzantine Rite.
The Polychronion is chanted for the secular authorities, the church authorities, individuals on specific occasions, and the whole community of Orthodox Christians.


There are two forms of the Polychronion in the Slavic usage:
The Polychronion as chanted for a sovereign is derived from the traditional Latin acclamation "Ad multos annos" accorded by the populace to Roman Emperors. The acclamation was continued in Byzantine times in partially hellenized form: "Immultos annos", before it was completely translated into the Greek form "Εἰς πολλὰ ἔτη":
Depending on circumstance, the names of other members of the reigning family can be added between the second and third lines, in the same form. Since there remain no Orthodox monarchies nowadays, the Polychronion is only chanted for ecclesiastical authorities, namely the Patriarch or diocesan bishop, in which case it is usually called the "Phēmē".