In music theory, a Neapolitan chord is a major chord built on the lowered second (supertonic) scale degree. It usually appears in the first inversion, thus conforming to the traditional classification of a sixth chord. Thus it is commonly known by the name Neapolitan sixth. In tonal harmony, the function of a Neapolitan chord is to prepare the dominant, substituting for the IV or ii chord. For example, it often precedes a perfect cadence, where it functions as a sub-dominant (IV).

The Neapolitan chord is so-called because it is erroneously attributed to 17th century Baroque composers in Naples, Italy, who used it at dramatic moments in their operas. Although the Neapolitan chord was used by these composers, it originated earlier.

The most common variation on the Neapolitan chord is the Neapolitan major seventh, which adds a major seventh to the chord (this happens to also be the tonic).