The Neapolitan triad is a major triad built on lowered scale degree 2 (Solfège: "ra" instead of "re"). It therefore contains scale degrees ↓2, 4, and ↓6 (Solfège: ra-fa-le). In most contexts, it appears in first inversion rather than root position, and it appears with a doubled bass rather than a doubled root. When in first inversion, scale degree ↓2 cannot be doubled because it is a tendency tone that must either immediately or soon resolve to the leading tone.

Different sources use different labels, most often either bII⁶ or N⁶. The flat symbol in front of the Roman numeral refers to lowering the root from "re" to "ra"; this may or may not involve a literal flat. The example below illustrates the Neapolitan triad in three different keys. Notice that the three chords involve a flat, a natural sign, and a double flat, respectively.

The Neapolitan chord is typically used in minor keys or in a passage where major is borrowing from minor. Like the supertonic chord, it has a predominant function. See the example progressions below.

i	VI	iv	bII6	cad64	V7	i
T	[T]	P	[P]	D	[D]	T

In a major key, you must alter two notes for the Neapolitan—scale degrees 2 and 6—in order to create a major triad.

I	vii°7	I	bVI	bII6	V	I
T	D	T	[T]	P	D	T