The oboe is a type of double reed woodwind instrument. Today, the oboe is commonly used as orchestral or solo instrument in symphony orchestras, concert bands, chamber ensembles and classical music. The oboe is widely recognized as the instrument that tunes the orchestra with its distinctive ‘A’.

The standard Baroque oboe is generally made of boxwood and has three keys: a “great” key and two side keys (the side key is often doubled to facilitate use of either the right or left hand on the bottom holes). In order to produce higher pitches, the player has to “overblow”, or increase the air stream to reach the next harmonic.

The Classical period brought a regular oboe whose bore was gradually narrowed, and the instrument became outfitted with several keys, among them those for the notes D♯, F, and G♯. A key similar to the modern octave key was also added called the “slur key”, though it was at first used more like the “flick” keys on the modern German bassoon. Only later did French instrument makers redesign the octave key to be used in the manner of the modern key (i.e. held open for the upper register, closed for the lower).

The narrower bore allows the higher notes to be more easily played, and composers began to more often utilize the oboe’s upper register in their works. Because of this, the oboe’s tessitura in the Classical era was somewhat broader than that found in Baroque works. The range for the

Classical oboe extends from C4 to F6 (using the scientific pitch notation system), though some German and Austrian oboes are capable of playing one half-step lower.

Classical-era composers who wrote concertos for oboe include Mozart (both the solo concerto in C major and the lost original of Sinfonia Concertante in E♭ major), Haydn, Beethoven, and numerous other composers including Johann Christian Bach, Johann Christian Fischer, Jan Antonín Koželuh, and Ludwig August Lebrun. Many solos exist for the regular oboe in chamber, symphonic, and operatic compositions from the Classical era.

Source: Wikipedia