In music and music theory augmentation is the lengthening or widening of rhythms, melodies, intervals, chords. The opposite is diminution (diminished).

A melody or series of notes is augmented if the lengths of the notes are prolonged. A melody originally consisting of four quavers (eighth-notes) for example, is augmented if it later appears with four crotchets (quarter-notes) instead. This technique is often used in contrapuntal music. It gives rise to the "canon in augmentation", in which the notes in the following voice are longer than those in the leading. The music of Johann Sebastian Bach provides examples of this application.

An interval is augmented if it is widened; an augmented chord is one which contains an augmented interval. Thus an augmented fifth, for example, is a half step wider than the perfect fifth, and an augmented chord is a major chord whose fifth has been raised a half step.