One of the unique features a harmonica offers is double row of free-standing reeds. A free-standing reed is attached to the instrument on one end with the opposite side standing "free" so that it may vibrate as air rushes around it. They are usually made of metal, plastic, or in rare instances wood. Stacking two reed plates allows the instrument to produce a tone as air is blown or drawn across it.

The standard diatonic 10-hole harmonica has a unique layout of pitches that can be traced back to Richter's "Vamper." Richter's layout was truly ingenious in that chords could be played at any position on the harmonica, but a full scale is located at the center of the harmonica so that melodies can be easily played. His design is the standard for all 10-hole diatonic instruments to this day.

There are, of course, other scale patterns available in harmonicas. Chromatic harmonicas allow the player to play in any key using one harmonica. Chromatic models provide the complete 12 note octave with all sharps and flats. In harmonicas of this style, each hole contains four reeds: two are for natural notes and two for chromatic notes. The reeds for chromatic notes are brought into operation by pushing a slide button on the side of the harmonica. This closes off the airflow from one set of reeds and permits the other set to vibrate freely. Harmonicas in natural minor and harmonic minor scales are available from the Tombo Company as well.

Harmonicas were originally intended to play simple melodies. The diatonic varieties originally available were designed specifically for this purpose. This style of playing is known as straight harp. In short, the song you are playing is in the same key as your harmonica and the blow notes are emphasized.. This style is well suited to folk songs like Oh Susanna, fiddle tunes, and other old time music forms.