A sonatina is literally a small sonata. As a musical term, "sonatina" has no single strict definition; it is rather a title applied by the composer to a piece that is in basic sonata form, but is shorter, lighter in character, or more elementary technically than a typical sonata.

Like many musical terms, sonatina is used inconsistently. The most common meaning is a short, easy sonata suitable for students, such as the piano sonatinas of Clementi. However, by no means are all sonatinas technically undemanding, for example the virtuoso sonatinas of Busoni, and the Sonatine of Ravel; whilst several of Beethoven's Piano Sonatas, such as Op.14 No.2 and Op.49 No.2, familiar to most intermediate students, could as well have been called sonatinas.

In general, a sonatina will have one or more of the following characteristics: brevity; fewer movements than the four of the late classical sonata; technical simplicity; a lighter, less serious character. The first (or only) movement is generally in an abbreviated sonata form, with little or no development of the themes. For this reason, a sonatina is sometimes defined, especially in British usage, as a short piece in sonata form in which the development section is entirely absent: the exposition is followed immediately by a brief bridge passage to modulate back to the home key for the recapitulation. Subsequent movements (at most two) may be in any of the common forms: e.g. a minuet or scherzo, a slow theme-and-variations, or a rondo.