In music, interpolation is an abrupt change of elements, with (almost immediate) continuation of the first idea. Another definition for interpolation can be located in William Caplin's textbook on classical form, in which he states that, in the context of a musical sentence or period, interpolation is "unrelated material inserted between two logically succeeding functions." (Caplin 255) Interpolation may also refer to borrowing.

This device is commonly used to extend what would normally be a regular phrase into an irregular and extended phrase. This expansion by interpolation is achieved by the addition of extra music in the middle of a phrase (commonly through the use of sequence). A clear example exists in the second movement of Mozart's Piano Sonata, K.330.

David Lynch has cited the musical concept of interpolation as the theme for his film Lost Highway .