Really neither English nor technically a horn, the cor anglais is a double reed woodwind musical instrument in the oboe family. It is actually a kind of tenor oboe, a transposing instrument pitched in F, a fifth lower than the more familiar orchestral oboe (a C instrument), and is consequently approximately one-third longer.

The fingering and playing technique used for the cor anglais are essentially the same as those of the oboe, with a sounding range stretching from the E (or, rarely, E flat) below middle C to the C two octaves above middle C.

Its pear-shaped bell gives it a somewhat more nasal, covered timbre than that of the oboe, being closer in tone quality to the oboe d'amore. Whereas the oboe is the soprano instrument of the oboe family, the cor anglais is generally regarded as the alto member of the family, and the oboe d'amore, pitched between the two in the key of A, is the mezzo-soprano member.

It is perceived to have a more mellow and more plaintive tone than the oboe. Its appearance differs from the oboe in that the reed is attached to a slightly bent metal tube called the bocal, or crook, and the bell has a bulbous shape.

Reeds used to play the cor anglais are similar to those used for an oboe, comprising a piece of cane folded in two. Although the instrument itself is longer, a cor anglais reed is shorter than that of an oboe reed, and also slightly wider. Where the cane on an oboe reed is connected to a small metal tube (the staple) partially covered in cork, there is no such cork on a cor anglais reed, which fits metal against metal onto the bocal, in a manner not dissimilar to the bassoon.

A very common explanation for the name of this instrument is that 'cor anglais' is actually a corruption of the phrase 'cor anglé'; however, this suggestion is strongly contested. English horns at one time did have curves or angles, but since the late 19th century straight-bodied instruments have become the rule, with a curve in the instruments' mouthpiece allowing the player to hold it close to their body.

In J.S. Bach's cantatas, early English horns appeared as oboe da caccia, a phrase linguistically related to hunting horns or corno da caccia. It has been suggested that the instrument's flared bell and sound which resembles a stopped (or muted) horn justifies its name.