In music, an ostinato (Italian: [ostiˈnaːto]; derived from Italian word for stubborn, compare English obstinate) is a motif or phrase that persistently repeats in the same musical voice, frequently in the same pitch. Well-known ostinato-based pieces include classical compositions such as Ravel's Boléro and the Carol of the Bells, and popular songs such as Donna Summer and Giorgio Moroder's "I Feel Love" (1977), Henry Mancini's theme from Peter Gunn (1959), The Who's "Baba O'Riley" (1971), and The Verve's "Bitter Sweet Symphony" (1997).

Both ostinatos and ostinati are accepted English plural forms, the latter reflecting the word's Italian etymology.

The repeating idea may be a rhythmic pattern, part of a tune, or a complete melody in itself. Strictly speaking, ostinati should have exact repetition, but in common usage, the term covers repetition with variation and development, such as the alteration of an ostinato line to fit changing harmonies or keys.

If the cadence may be regarded as the cradle of tonality, the ostinato patterns can be considered the playground in which it grew strong and self-confident.

Within the context of film music, Claudia Gorbman defines an ostinato as a repeated melodic or rhythmic figure that propels scenes that lack dynamic visual action.

Ostinati play an important part in improvised music (rock and jazz), in which they are often referred to as riffs or vamps. A "favorite technique of contemporary jazz writers", ostinati are often used in modal and Latin jazz and traditional African music including Gnawa music.

The term ostinato essentially has the same meaning as the medieval Latin word pes, the word ground as applied to classical music, and the word riff in contemporary popular music.