Tempo rubato (Italian for 'stolen time'; UK: /ˈtɛmpoʊ rʊˈbɑːtoʊ/, US: /ruː-/, Italian: [ˈtɛmpo ruˈbaːto];) is a musical term referring to expressive and rhythmic freedom by a slight speeding up and then slowing down of the tempo of a piece at the discretion of the soloist or the conductor. Rubato is an expressive shaping of music that is a part of phrasing.

While rubato is often loosely taken to mean playing with expressive and rhythmic freedom, it was traditionally used specifically in the context of expression as speeding up and then slowing down the tempo. In the past, expressive and free playing (beyond only rubato) was often associated with the terms "ad libitum". Rubato, even when not notated, is often used liberally by musicians, e.g. singers frequently use it intuitively to let the tempo of the melody expressively shift slightly and freely above that of the accompaniment. This intuitive shifting leads to rubato's main effect: making music sound expressive and natural. Nineteenth century composer-pianist Frédéric Chopin is often mentioned in the context of rubato (see Chopin's technique and performance style and his adaptation of the bel canto idiom).

The term rubato existed even before the romantic era. In the 18th century, rubato meant expressing rhythm spontaneously, with freedom. In many cases, it was achieved by playing uneven notes. This idea was used, among others, by Ernst Wilhelm Wolf and Carl Philipp Emanuel Bach. In addition to that, Leopold Mozart claimed that the accompaniment should remain strictly in tempo.

In the mid 18th century, the meaning of rubato began to change gradually. People were using the term as being able to move notes freely back and forth. Johann Friedrich Agricola interpreted rubato as "stealing the time".

As time moved on to the 19th century, rubato became recognized slightly differently. In Chopin's music, rubato functioned as a way to make a melody more emotional through changing the tempo by, for instance, accelerando, ritenuto and syncopations. Chopin "often played with the melody subtly lingering or passionately anticipating the beat while the accompaniment stayed at least relatively, if not strictly, in time". In this case, rubato is used as a concept of flexibility of tempo for a more expressive melody.

One can distinguish two types of rubato: in one the tempo of the melody is flexible, while the accompaniment is kept in typical regular pulse (yet not rigidly in mechanical fashion; but adjusting to the melody as necessary—see below). Another type affects melody and accompaniment. While it is often associated with music of the Romantic Period, classical performers frequently use rubato for emotional expressiveness in all kinds of works.

Tempo rubato (or a tempo rubato) means literally in robbed time, i.e., duration taken from one measure or beat and given to another, but in modern practice the term is quite generally applied to any irregularity of rhythm or tempo not definitely indicated in the score.
The terms ad libitum, (ad lib.), a piacere, and a capriccio, also indicate a modification of the tempo at the will of the performer. Ad libitum means at liberty; a piacere, at pleasure; and a capriccio, at the caprice (of the performer).

— Music notation and terminology (1921) by Karl Wilson Gehrkens