Ut queant laxis

Ut queant laxis or Hymnus in Ioannem is a Latin hymn in honour of John the Baptist written in Horatian Sapphics and traditionally attributed to Paulus Diaconus, the eighth-century Lombard historian. It is famous for its part in the history of musical notation, in particular solmization. The hymn is sung to a Gregorian chant, the original do-re-mi music.

The chant is useful for teaching singing because of the way it uses successive notes of the scale: the first six musical phrases of each stanza begin on a successively higher notes of the hexachord, giving ut–re–mi–fa–so–la; though ut is replaced by do in modern solfège. The naming of the notes of the hexachord by the first syllable of each hemistich (half line of verse) of the first verse is usually attributed to Guido of Arezzo. Guido, who was active in the eleventh century, is regarded as the father of modern musical notation. He made use of clefs (C & F clefs) and invented the ut-re-mi-fa-sol-la-si notation. The hymn does not help with the seventh tone as the last line, Sancte Iohannes, breaks the ascending pattern. The syllable si, for the seventh tone, was added in the 18th century.

It is not known who wrote the melody. Guido possibly composed it, but he more likely used an existing melody. A variant of the melody appears in an eleventh-century musical setting of Horace's poem Ode to Phyllis () recorded in a manuscript in France. The hymn uses classical metres: the Sapphic stanza consisting of three Sapphic hendecasyllables followed by an adonius (a type of dimeter).

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