A da capo aria is in ternary form, meaning it is in three sections. The first section is a complete musical entity, ending in the tonic key, and could in principle be sung alone. The second section contrasts with the first in its musical texture, mood, and sometimes also tempo. The third section was usually not written out by the composer, who rather simply specified the direction "da capo" (Italian for "from the beginning"), which meant that the first section should be repeated in full.
The da capo aria depended for its success on the ability of the singer to improvise variations and ornaments during the third section, to keep it from being a mere repetition of the first. This was especially so for da capo arias written in slower tempos, where the opportunity to improvise, as well as the risk of dullness, were greater. The ability to improvise variations and ornaments was a skill learned by, and expected of, all solo singers. The decline in this ability following the Baroque era is perhaps the reason why the da capo aria ultimately acquired a reputation as a musically dull form. The authentic performance movement, starting in the mid twentieth century, restored improvisation to the performance of da capo arias, although the practice has yet to become universal even among authentic performance artists.
Handel's oratorio Messiah (1742) includes two well-known da capo arias, "He Was Despised" (for alto soloist) and "The Trumpet Shall Sound" (for bass). J. S. Bach's famous cantata Jauchzet Gott in allen Landen (BWV 51, 1730) begins with a flamboyant da capo aria for soprano, trumpet soloist, and strings.