In medieval music, conductus (plural: conductus) is a type of sacred, but non-liturgical vocal composition for one or more voices. The word derives from Latin conducere (to escort), and the conductus was most likely sung while the lectionary was carried from its place of safekeeping to the place from which it was to be read. The conductus was one of the principal types of vocal composition of the ars antiqua period of medieval music history.
The form most likely originated in the south of France around 1150, and reached its peak development during the activity of the Notre Dame School in the early 13th century. Most of the conductus compositions of the large mid-13th-century manuscript collection from Notre Dame are for two or three voices. Much of the surviving repertoire is contained in the Florence Manuscript and also the manuscript Wolfenbüttel 1099. Conductus are also unique in the Notre Dame repertory in admitting secular melodies as source material, though sacred melodies were also commonly used. Common subjects for the songs were lives of the saints, feasts of the Lord, the Nativity, as well as more current subjects such as exemplary behavior of contemporary witnesses to the faith, such as Thomas Becket. A significant and interesting repertory of conductus from late in the period consists of songs which criticize abuses by the clergy, including some which are quite outraged. While it might be difficult to imagine them being sung in church, it is possible that the repertory may have had an existence beyond its documented liturgical use.
The style of the conductus was usually rhythmic, as befitting music accompanying a procession, and almost always note-against-note. Stylistically it was utterly different from the other principal liturgical polyphonic form of the time, organum, in which the voices usually moved at different speeds; in conductus, the voices sang together, in a style also known as discant.
Music theorists who wrote about the conductus include Franco of Cologne, who advocated having a beautiful melody in the tenor, Johannes de Garlandia, and Anonymous IV. Early 14th century theorist Jacques of Liège, a vigorous defender of the ars antiqua style against the new "immoral and lascivious" ars nova style, lamented the disinterest of contemporary composers in the conductus. The conductus lasted longest in Germany, where it was documented into the 14th century.
English conductus of the late thirteenth and early fourteenth centuries often use the technique of rondellus.