A kontakion (Greek κοντάκιον, kondákion, plural κοντάκια, kondákia) is a form of hymn in the Byzantine liturgical tradition. The kontakion form originated in Syriac hymnography and gained prominence in Byzantium during the 6th century, particularly through the work of St. Romanos the Melodist of Emesa. Kontakia have a number of strophes (oikoi or ikoi, stanzas; singular oikos or ikos) and begin with a prologue (the prooimoion or koukoulion). A kontakion sometimes has a biblical theme and may feature a dialogue between biblical characters. The only kontakion that is used in full length today is the Akathist to the Theotokos.

The word kontakion derives from the Greek κόνταξ (kóntax), which means "rod" or "stick" and refers specifically to the rod around which a scroll is wound. While the genre dates to at least the 6th century, the word itself is attested only in the 9th century. The name is likely a reference to the fact that kontakions tend to be lengthy and have a large number of stanzas, thus metaphorically or literally requiring a great deal of "scrolling".

A hymn book containing kontakia is called a kontakarion (κοντακάριον; loaned into Slavonic as kondakar, Church Slavonic: кондакарь), but a kontakarion is not just a collection of kontakia: in the tradition of the Cathedral Rite (like that practiced at the Hagia Sophia of Constantinople) this became the name of the book of the prechanter or lampadarios, also known as psaltikon, which contained all the soloistic parts of hymns sung during the morning service and the Divine Liturgy. Because the kontakia were usually sung by protopsaltes during the morning services, the first part for the morning service with its prokeimena and kontakia was the most voluminous part, and acquired the name kontakarion.

Originally the kontakion was a Syriac form of poetry,^{[citation needed]} achieving popularity in Constantinople first under Romanos the Melodist, Anastasios, and Kyriakos in the 6th century, and then under Sergius I of Constantinople and Sophronius of Jerusalem in the 7th century. Romanos' works had been widely acknowledged as a crucial contribution to Byzantine hymnography, in some kontakia he also supported Emperor Justinian by writing state propaganda.

Romanos' kontakion On the Nativity of Christ was also mentioned in his vita. Until the twelfth century, it was sung every year at the imperial banquet on that feast by the joint choirs of Hagia Sophia and of the Church of the Holy Apostles in Constantinople. Most of the poem takes the form of a dialogue between the Mother of God and the Magi.

A kontakion is a poetic form frequently encountered in Byzantine hymnography. It was probably based on Syriac hymnographical traditions, which were transformed and developed in Greek-speaking Byzantium. It was a homiletic genre and could be best described as a "sermon in verse accompanied by music". In character it is similar to the early Byzantine festival sermons in prose — a genre developed by Ephrem the Syrian — but meter and music have greatly heightened the drama and rhetorical beauty of the speaker's often profound and very rich meditation.

Medieval manuscripts preserved about 750 kontakia since the 9th century, about two thirds had been composed since the 10th century, but they were rather liturgical compositions with about two or six oikoi, each one concluded by a refrain identical to the introduction (prooimion). Longer compositions were the Slavic Akafist which were inspired by an acrostic kontakion whose 24 stanzas started with each letter of the alphabet (Akathist).

Within the cathedral rite developed a truncated form which reduced the kontakion to one oikos or just to the prooimion, while the music was elaborated to a melismatic style. The classical repertoire consisted of 42 kontakia-idiomela, and 44 kontakia-prosomoia made about a limited number of model stanzas consisting of fourteen prooimia-idiomela and thirteen okoi-idiomela which could be combined independently. This classical repertoire was dominated by classical composers of the 6th and 7th centuries.