"Ut queant laxis" or "Hymnus in Ioannem" is a Latin hymn in honor of John the Baptist, written in Horatian Sapphics with text 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 belongs to the tradition of Gregorian chant.

Quintus Horatius Flaccus, commonly known in the English-speaking world as Horace, was the leading Roman lyric poet during the time of Augustus. The rhetorician Quintilian regarded his Odes as just about the only Latin lyrics worth reading: "He can be lofty sometimes, yet he is also full of charm and grace, versatile in his figures, and felicitously daring in his choice of words."