A piano trio is a group of piano and two other instruments, almost always a violin and a cello, or a piece of music written for such a group. It is one of the most common forms found in classical chamber music.

Traditionally, piano trios tend to be in the same overall form as a sonata, which can be roughly said to be as follows:

However, many variations on this form exist, and there are piano trios which bear no resemblance to this formal plan.

Among the better known piano trios in classical music are Ludwig van Beethoven's Ghost (1808) and Archduke (1811) trios, Joseph Haydn's Gypsy Rondo trio, and Antonin Dvorak's Dumky trio (1891). Other fairly well known examples exist by Franz Schubert, Johannes Brahms and Dmitri Shostakovich. Many other composers have also worked in the form.

Although the grouping of piano, violin and cello is by far the most common in piano trios, the name is sometimes also used to describe other works for piano and two other instruments. Examples include Wolfgang Amadeus Mozart's Kegelstatt trio, for clarinet, viola and piano and Bela Bartok's three-movement work, Contrasts, for piano, clarinet and violin.

The term piano trio can also refer to a group of musicians who regularly play together. Among the best known such groups were the one consisting of Alfred Cortot, Jacques Thibaud and Pablo Casals and the Beaux Arts Trio. A more recent well-known trio consists of Emanuel Ax, Young Uck Kim, and Yo-Yo Ma.