The alto clef assigns the note middle C to the middle line of the staff. The alto clef is currently used by only one modern instrument: the viola--and for this reason is sometimes called the viola clef. It was formerly used by the trombone--Russian composers persisted in this practice well into the twentieth century, and is found in music written for the tenor viola da gamba. It was also used in some older vocal music. An acceptable hand-written version of the alto clef (and tenor clef as well) somewhat resembles the letter "K".

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The treble clef

The treble clef assigns the G above middle C to the 2nd line from the bottom of the staff.

Most woodwind instruments read treble clef (even low-pitched transposing instruments), as well as high brass, violins, and tuned percussion. Violas and cellos occasionally use the treble clef to avoid excessive ledger lines in extended high passages. On the piano, the right hand usually is written in treble clef, while the left hand is written in bass clef. In vocal music, both Soprano and Contralto parts now use the treble clef, whereas in former centuries they would have each used their own clef.