In ecclesiastical terminology signifies the order or arrangement of the Divine Office (perhaps because the parts are closely connected and follow in order) and also, in a wide sense, the Office itself. The Acolouthia is composed of musical and rhetorical elements, the first usually given in the musical mode or tone (Ἠχος), according to which the liturgical compositions are chanted. There are eight modes, four primary and four secondary. As the Greeks rarely used texts set to musical notation, they learned by heart the words and music of some standard hymn or canticle, and this served as a model for other hymns of the same rhythm. A strophe or stanza of a standard hymn which indicates the melody of a composition, is known as a hirmos (ἑιρμός). Some believe that a hirmos placed at the end of a hymn should be called a catabasia (καταβασία) while others hold that the catabasia is a short hymn sung by the choir, who descend from their seats into the church for the purpose. The fundamental element of the Acolouthia is the troparion (τροπάριον), which is a short hymn, or one of the stanzas of a hymn. The contakion (κοντάκιον) is a troparion which explains briefly the character of the feast celebrated in the day's Office. The oikos (oἶκος) is a somewhat longer troparion, which in concise style glorifies the virtues and merits of the subject of the feast. The apolytikion (ἀπολυτίκων) is a troparion which is proper to the day, and is said just before the prayer of dismissal.

The ode (ᾠδή) was originally one of the nine inspired canticles sung in the morning Office, but later the name was also given to uninspired compositions, consisting of a varying number of poetical troparia and modelled after the Scriptural odes. Such odes are often combined to form a canon (κανών) which is usually composed of nine, but sometimes of a smaller number of odes. Finally, the stichos (στίχος) is a short verse taken from the Psalms or some other book of Holy Scripture, while the sticheron (στίχηρον) is a short verse of ecclesiastical composition modelled after the stichos. The parts of the Office are the Little Vespers, the Greater Vespers, the Orthros (dawn), the four little Hours, and the Apodeipnon (compline). The Little Vespers, which are recited before sunset, consist of the invitatory versicles, Psalms 103 and 140, several stichoi and similar stichera, a short hymn, and a psalm, some similar stichera and stichoi, the Nunc dimittis, the trisagion, and the apolytikion.

Greater Vespers, which are said after sunset, begin with the invitatory, Psalm 103 and the greater litany, and then the priest says the prayers of the Lychnic. The choir recites the first cathisma (division of the psalter), and after the deacon has said the litany it chants Psalm 140, and several versicles during the incensation. After changing his vestments in the sacristy, the priest says the prayer for the entrance, the deacon after some versicles recites the litanies, and the priest says the prayer of benediction. During the procession to the narthex, stichera proper to the feast are recited, and then the priest recites a series of prayers, to which the choir answers Kyrie Eleison many times, and the priest blesses all present. Next the stichera proper to the feast are said by the choir with the Nunc dimittis, the trisagion, a prayer to the Trinity, the Lord's Prayer, and the apolytikion, and Vespers are concluded with lessons from the Scriptures. The first part of the Orthros, or midnight office, consists of twelve prayers, the greater litany, two stichera followed by Psalms 134 and 135, a third sticheron followed by the gradual psalms, an antiphon with the prokeimenon, the reading of the Gospel, many acclamations and three canons of odes, while the second part of the Orthros, corresponding to Lauds in the Roman Office, is composed of Psalms 148, 149, 150, several similar stichera, the greater doxology, a benediction, and the prayer for the dismissal.

Each little Hour is followed by a supplementary hour, called a Μεσώριον. Prime begins with the recitation of three psalms followed by a doxology, two stichoi, a doxology, a troparion in honour of the Theotokos (the Birthgiver of God, i.e. the Blessed Virgin), the trisagion, several variable troparia, the doxology and dismissal, while its supplementary Hour is composed of a troparion, doxology, troparion of the Theotokos, Kyrie Eleison repeated forty times, a prayer, and a doxology. Terce, Sext, and None each contain the invitatory versicles, three psalms, a doxology, two stichoi, a doxology, the troparion of the Theotokos, the trisagion, doxology, another troparion of the Blessed Virgin, and the Kyrie Eleison repeated forty times, and their Mesoria have the invitatory versicles, three psalms, a doxology, troparion, doxology, troparion of the Theotokos, Kyrie Eleison repeated forty times, and a proper prayer.

Before or after None, an office called Τὰ τυπικά is recited, which consists ordinarily of the invitatory versicles, Psalms 102 and 145, and a troparion, but in the seasons of fasting this Office is regulated by different rubrics. The last part of the Office is called the Apodeipnon and corresponds to the Roman Compline. The greater Apodeipnon is said during Lent, the little Apodeipnon during the rest of the year. The latter is composed of a doxology, troparion, the trisagion, the Lord's Prayer, the Kyrie Eleison repeated twelve times, and invitatory versicles, and Psalms 50, 69, and 162, which are followed by the greater doxology, the Creed, the trisagion, the Lord's Prayer, the troparion proper to the feast, the Kyrie Eleison repeated forty times, several invocations, and the long prayers of dismissal.

RAYAEUS, Tractatus de Acolouthia, etc., in Acta SS., June II, 13; LECLERCQ in Dict. d'archéol. chrét., II., 340; NEALE, History of the Holy Eastern Church (London, 1850).

J.F. GOGGIN