The cornettino (Italian, plural cornettini; German: Diskant Zink, Quart-Zink) is the small descant instrument of the cornett family of lip-reed wind instruments, a fourth or fifth higher than the larger, more common treble cornett. Cornettini were built in two sizes, usually described as in D or C, although the note sounded with all finger-holes covered is E or D, respectively, which can be lowered a further whole tone to D or C by slackening the embouchure. The name cornettino in Italian means a small cornetto, which in turn means "small horn".

Surviving specimens of cornettino are 35 to 37 centimetres (14 to 15 in) long for the earlier higher pitched instrument in D, and 39 to 46 cm (15 to 18 in) for the instrument in C. The treble cornetts in G range from 51 to 63 cm (20 to 25 in) in length. These large variations of instrument lengths are mostly due to the variation of pitch standards that prevailed in Europe at different times and places, with A₄ ranging from 415 to 510 Hz. Like organs and trombones, the cornettino was regarded as primarily a church instrument, and hence was constructed in Chor-ton (choir pitch) at the height of its popularity in the 17th century, which was around 466 Hz.

Like the cornetto, the cornettino was usually made from two lengthwise halves of wood, often walnut or boxwood, with the bore carved out and glued together. The instrument was then tightly covered with black-dyed leather or parchment to prevent leaks and improve the grip for the player. The mouthpieces were made from animal horn, bone or ivory.

Some German-made instruments featured decorative ferrules of silver, gold, or gold-plated brass at one or both ends of the instrument, to prevent the fraying of the leather or parchment. A small number of surviving cornettini were made from ivory, usually highly ornamented with decorative carved designs.

Modern replica instruments are made by a small number of historical instrument manufacturers, some using modern composite materials or epoxy resin, pioneered by Christopher Monk in the mid-20th century revival of the cornett.

Three mute cornettini survive, one in Nuremberg and two in Vienna (id est descant mute cornetti). These instruments are straight, like their treble counterparts, with an integral mouthpiece. No extant music for the mute cornettino has yet come to light and the function of this instrument remains obscure. The surviving score of the large scale madrigal, Udite chiari e generosi figli à 16 voci, by Giovanni Gabrieli, requires a cornetto muto on the cantus line of Choro I. Since this part requires the instrument to play up to A₅, a mute cornettino may have been intended by the composer - certainly this part would be readily playable on such an instrument, although, the tessitura of the part is well within the compass of a regular mute cornett in G or F.

Cornettini were common in the high Renaissance and the Baroque musical periods. They were featured extensively in Northern European music and ignored almost entirely by Southern European composers, except those who migrated north. In the time of Michael Praetorius, the cornettino seems to have sometimes been used in sacred vocal music to play in unison with voices (especially tenors) an octave higher. Later in the 17th century, Northern European composers frequently used cornettini in large scale Masses, cantatas and other sacred music. The cornettino was favoured by the Stadtpfeiffen and composers like Johann Caspar Horn and Matthias Spiegler wrote a significant quantity of consort music featuring one to three cornettini. It appears that the cornettino continued to be used, primarily in church music and in Stadtpfeiffer bands, in some places in Europe until the late 18th century. Georg Philipp Telemann and Johann Sebastian Bach used the cornettino in several church cantatas.

The tessitura of the cornettino is C₄ (middle C) to around G₅, although a competent player with a strong embouchure can play higher; the highest note in the repertoire is E₆.