A sestina (Italian: sestina, from sesto, sixth; Old Occitan: cledisat [klediˈzat]; also known as sestine, sextine, sextain) is a fixed verse form consisting of six stanzas of six lines each, normally followed by a three-line envoi. The words that end each line of the first stanza are used as line endings in each of the following stanzas, rotated in a set pattern.

The invention of the form is usually attributed to Arnaut Daniel, a troubadour of 12th-century Provence, and the first sestinas were written in the Occitan language of that region. The form was cultivated by his fellow troubadours, then by other poets across Continental Europe in the subsequent centuries; they contributed to what would become the "standard form" of the sestina. The earliest example of the form in English appeared in 1579, though they were rarely written in Britain until the end of the 19th century. The sestina remains a popular poetic form, and many sestinas continue to be written by contemporary poets.