Extended chords are tertian chords (built from thirds) or triads with notes extended, or added, beyond the seventh, including all the thirds in between the seventh and the extended note. Thus ninth, eleventh, thirteenth, and all farther chords are extended chords.

In popular music and jazz music, these chords are often referred to as added note chords, and are referred to by the simple interval rather than the compound interval (i.e., "added sixth chord" as opposed to "thirteenth chord").

In practice however, extended chords do not typically use all the chord members; the fifth is often omitted, as are notes between the seventh and the highest note (i.e., the ninth is omitted in an eleventh chord, the ninth and eleventh are omitted in a thirteenth chord).

Extended chords are rarely seen in the Baroque era, and are uncommon in the Classical era. When used in the Romantic era, they were almost always found on the dominant scale degree (as V⁹, V¹¹, and V¹³).

Performance

When playing extended chords on instruments which are limited to four or less tones it is important to select which notes to play so as to still give the sonority or effect as the intended extended chord. Always play the root, third, seventh, and the most extended note if possible. The root is the central note of the chord, the third defines the chord's quality as minor or major, the extended note is what makes the chord extended, and the seventh defines the chord as an extended chord and not an added note chord. Any notes which happen to be altered, such as a flatted ninth, would also need to be included. Thus in a thirteenth chord one would play the root, third, seventh, and thirteenth, and be able to leave out the fifth, ninth, and eleventh.