D'ETTO. — The term (a diminutive of *duo*) does not properly denote a musical genre, but rather various types of compositions consisting of two voices or parts.
In modern common usage, it signifies a piece for two voices with instrumental accompaniment, more rarely as an independent composition, and more frequently as a lyrical or dramatic moment in a theatrical work.
A particular aspect of the *d'etto* is that of a religious character, as seen, without instrumental accompaniment, in the *Bicinia* of the 16th century, while in the *Concerti ecclesiastici* of Viadrina it appears with continuo bass accompaniment and in a concertante or imitative style. In the secular sphere, the chamber *d'etto* held notable prominence in the 17th and 18th centuries, especially in Italy, where it was cultivated by F. Rasi, P. Quagliati, A. Stradella, G. B. Bononcini, A. Steffani, and G. M. Clari; in modern times, the duets of Mendelssohn are to be remembered. A final meaning of *d'etto* coincides with that of an instrumental composition for two instruments of the same type (e.g., for two violins) with a concertante character if with orchestra, or with a soloistic character if akin to the form of the sonata.