Credited to Giacomo da Lentini of the Sicilian School at Emperor Frederick II's court in Palermo, taking its name from the Italian sonetto ('little song').
The Italian (Petrarchan) sonnet pairs an eight-line octave (typically ABBA ABBA) with a six-line sestet (CDECDE or CDCCDC), pivoting in argument or mood at the ninth-line volta.
Adapted into 16th-century English verse, where the Shakespearean form uses three quatrains and a closing rhymed couplet (ABAB CDCD EFEF GG) in iambic pentameter.