Many concerto movements are in ritornello form, from ritornello, the name for the orchestral music that typically starts the movement off. Contrast is basic to the concerto, and ritornello form focuses on contrast between two musical ideas, or groups of ideas — one belonging to the orchestra and the other to the soloist. The orchestral material (the ritornello) tends to be solid and forceful, the solo material faster and more brilliant.

Ritorno, the Italian word for “return,” tells us that the function of the ritornello in ritornello form is to return many times as a stable element of the form. Usually it returns only in part, and usually it is played in different keys as the movement proceeds. As for the musical ideas for the solo, sometimes these are virtuoso passages, sometimes themes, sometimes larger sections including themes and other material. To end the movement, the orchestral ritornello returns in the tonic key and, often, at full length.

Ritornello form can be diagrammed as follows, where RIT stands for the entire ritornello; [RIT] for any part of the ritornello; and Solo 1, 2, 3, etc., for the solo sections:

We need not worry too much about the exact number of ritornello fragments, the keys, and other details shown in such form diagrams; these change from concerto to concerto. More important is the general impression that the form gives: the sense of a sturdy, reliable support in the orchestra for rapid and sometimes fantastic flights by the solo or solo group. Alongside the almost improvisational freedom of the solo instruments, the ritornello is always there, ready to bring them back down to earth and remind us of the original point of departure.