The cornet (ˈkɔːrnᵻt, kɔːrˈnɛt) is a brass instrument similar to the trumpet but distinguished from it by its conical bore, more compact shape, and mellower tone quality. The most common cornet is a transposing instrument in B. There is also a soprano cornet in E and cornets in A and C. All are unrelated to the Renaissance and early Baroque cornett.
The cornet was derived from the posthorn by applying rotary valves to it in the 1820s, in France. However, by the 1830s, Parisian makers were using piston valves. Cornets first appeared as separate instrumental parts in 19th-century French compositions.
The instrument could not have been developed without the improvement of piston valves by Silesian horn players Friedrich Blühmel (or Blümel) and Heinrich Stölzel, in the early 19th century. These two instrument makers almost simultaneously invented valves, though it is likely that Blühmel was the inventor, while Stölzel developed a practical instrument. They were jointly granted a patent for a period of ten years. François Périnet received a patent in 1838 for an improved valve, which became the model for modern brass instrument piston valves. The first notable virtuoso player was Jean-Baptiste Arban, who studied the cornet extensively and published La grande méthode complète de cornet à piston et de saxhorn, commonly referred to as the Arban method, in 1864. Up until the early 20th century, the trumpet and cornet co-existed in musical ensembles; symphonic repertoire often involves separate parts for trumpet and cornet. As several instrument builders made improvements to both instruments, they started to look and sound more alike. The modern-day cornet is used in brass bands, concert bands, and in specific orchestral repertoire that requires a more mellow sound.
The name "cornet" derives from the French corne, meaning "horn", itself from Latin cornu. While not musically related, instruments of the Zink family (which includes serpents) are named "cornetto" or "cornett" in modern English, to distinguish them from the valved cornet described here.