The cornet was invented by adding valves to the post horn around 1828.
 The valves allowed for melodic playing throughout the register of the cornet.
Trumpets were slower to adopt the new valve technology, so for the next 100 years or more, composers often wrote separate parts for trumpet and cornet.
The trumpet would play fanfare-like passages, while the cornet played more melodic passages.
The modern trumpet has valves that allow it to play the same notes and fingerings as the cornet.

Cornets and trumpets made in a given key (usually the key of B♭) play at the same pitch, and the technique for playing the instruments is nearly identical.
 However, cornets and trumpets are not entirely interchangeable, as they differ in timbre.
Also available, but usually seen only in the brass band, is an E♭ soprano model, pitched a fourth above the standard B♭.

Unlike the trumpet, which has a cylindrical bore up to the bell section, the tubing of the cornet has a mostly conical bore, starting very narrow at the mouthpiece and gradually widening towards the bell.
Cornets following the 1913 patent of E.A. Couturier can have a continuously conical bore.
The conical bore of the cornet is primarily responsible for its characteristic warm, mellow tone, which can be distinguished from the more penetrating sound of the trumpet.
The conical bore of the cornet also makes it more agile than the trumpet when playing fast passages, but correct pitching is often less assured.
The cornet is often preferred for young beginners as it is easier to hold, with its centre of gravity much closer to the player.

The cornet mouthpiece has a shorter and narrower shank than that of a trumpet so it can fit the cornet's smaller mouthpiece receiver.
The cup size is  often deeper than that of a trumpet mouthpiece.

One variety is the short model traditional cornet, also known as a "Shepherd's Crook" shaped model.
These are most often large–bore instruments with a rich mellow sound.
There is also a long-model or "American-wrap" cornet, often with a smaller bore and a brighter sound, which is produced in a variety of different tubing wraps and is closer to a trumpet in appearance.
The Shepherd's Crook model is preferred by cornet traditionalists.
The long-model cornet is generally used in concert bands in the United States, but has found little following in British-style brass and concert bands.
A third and relatively rare variety—distinct from the long-model or "American-wrap" cornet—is the "long cornet", which was produced in the mid-20th Century by C.G. Conn and F.E. Olds and visually is nearly indistinguishable from a trumpet except that it has a receiver fashioned to accept cornet mouthpieces.
The cornet was invented by adding valves to the post horn around 1828.  The valves allowed for melodic playing throughout the register of the cornet. Trumpets were slower to adopt the new valve technology, so for the next 100 years or more, composers often wrote separate parts for trumpet and cornet. The trumpet would play fanfare-like passages, while the cornet played more melodic passages. The modern trumpet has valves that allow it to play the same notes and fingerings as the cornet.
Cornets and trumpets made in a given key (usually the key of B♭) play at the same pitch, and the technique for playing the instruments is nearly identical.  However, cornets and trumpets are not entirely interchangeable, as they differ in timbre. Also available, but usually seen only in the brass band, is an E♭ soprano model, pitched a fourth above the standard B♭.
Unlike the trumpet, which has a cylindrical bore up to the bell section, the tubing of the cornet has a mostly conical bore, starting very narrow at the mouthpiece and gradually widening towards the bell. Cornets following the 1913 patent of E.A. Couturier can have a continuously conical bore. The conical bore of the cornet is primarily responsible for its characteristic warm, mellow tone, which can be distinguished from the more penetrating sound of the trumpet. The conical bore of the cornet also makes it more agile than the trumpet when playing fast passages, but correct pitching is often less assured. The cornet is often preferred for young beginners as it is easier to hold, with its centre of gravity much closer to the player.
The cornet mouthpiece has a shorter and narrower shank than that of a trumpet so it can fit the cornet's smaller mouthpiece receiver. The cup size is  often deeper than that of a trumpet mouthpiece.
One variety is the short model traditional cornet, also known as a "Shepherd's Crook" shaped model. These are most often large–bore instruments with a rich mellow sound. There is also a long-model or "American-wrap" cornet, often with a smaller bore and a brighter sound, which is produced in a variety of different tubing wraps and is closer to a trumpet in appearance. The Shepherd's Crook model is preferred by cornet traditionalists. The long-model cornet is generally used in concert bands in the United States, but has found little following in British-style brass and concert bands. A third and relatively rare variety—distinct from the long-model or "American-wrap" cornet—is the "long cornet", which was produced in the mid-20th Century by C.G. Conn and F.E. Olds and visually is nearly indistinguishable from a trumpet except that it has a receiver fashioned to accept cornet mouthpieces.
Cornet