A nonchord tone (NCT), nonharmonic tone, or embellishing tone is a note in a piece of music or song that is not part of the implied or expressed chord set out by the harmonic framework. In contrast, a chord tone is a note that is a part of the functional chord. Nonchord tones are most often discussed in the context of the common practice period of classical music, but the term can also be used in the analysis of other types of tonal music, such as Western popular music.

Nonchord tones are often categorized as accented non-chord tones and unaccented non-chord tones depending on whether the dissonance occurs on an accented or unaccented beat (or part of a beat).

Over time, some musical styles assimilated chord types outside of the common-practice style. In these chords, tones that might normally be considered nonchord tones are viewed as chord tones, such as the seventh of a minor seventh chord. For example, in 1940s-era bebop jazz, an F♯ played with a C ⁷ chord would be considered a chord tone if the chord were analyzed as C^7(♯11). In European classical music, "[t]he greater use of dissonance from period to period as a result of the dialectic of linear/vertical forces led to gradual normalization of ninth, eleventh, and thirteenth chords [in analysis and theory]; each additional non-chord tone above the foundational triad became frozen into the chordal mass."

Chord and nonchord tones are defined by their membership (or lack of membership) in a chord: "The pitches which make up a chord are called chord-tones: any other pitches are called non-chord-tones." They are also defined by the time at which they sound: "Nonharmonic tones are pitches that sound along with a chord but are not chord pitches." For example, if an excerpt from a piece of music implies or uses a C-major chord, then the notes C, E and G are members of that chord, while any other note played at that time (e.g., notes such as F♯) is a nonchord tone. Such tones are most obvious in homophonic music but occur at least as frequently in contrapuntal music.

According to Music in Theory and Practice, "Most nonharmonic tones are dissonant and create intervals of a second, fourth or seventh", which are required to resolve to a chord tone in conventional ways. If the note fails to resolve until the next change of harmony, it may instead create a seventh chord or extended chord. While theoretically in a three-note chord, there are nine possible nonchord tones in equal temperament, in practice nonchord tones are usually in the prevailing key. Augmented and diminished intervals are also considered dissonant, and all nonharmonic tones are measured from the bass note, or lowest note sounding in the chord except in the case of nonharmonic bass tones.

Nonharmonic tones generally occur in a pattern of three pitches, of which the nonharmonic tone is the center:

Nonchord tones are categorized by how they are used. The most important distinction is whether they occur on a strong or weak beat and are thus either accented or unaccented nonchord tones. They are also distinguished by their direction of approach and departure and the voice or voices in which they occur and the number of notes they contain.

An anticipation (ANT) occurs when this note is approached by step and then remains the same. It is basically a note of the second chord played early. In the example below, the dissonant B in bar 1 is approached by step and resolves when that same pitch becomes a chord tone in bar 2.