In music, a register is the relative "height" or range of a note, set of pitches or pitch classes, melody, part, instrument or group of instruments. For examples, violins are in a higher register than cellos. A higher register indicates higher pitch.

The register in which an instrument plays, or thus in which a part is written, affects the quality of sound or timbre. Register is also used stucturally in musical form, with the climax of a piece usually being in the highest register of that piece. Often serial and other pieces will use fixed register, allowing a pitch class to be expressed through only one pitch.