The harmonica is based on an ancient instrument, the sheng. A Chinese gourd and reed instrument, the sheng may have been invented as long as 5000 years ago by Chinese Empress Nyu-kwa. The basic design of the sheng allowed tones to be made while blowing or drawing air through the instrument making it unique among the ancient wind instruments.

Instruments resembling the modern harmonica had their genesis in the early 19th century. Christian Friedrich Ludwig Buschmann bundled fifteen pitch pipes into a roughly square shape, approximately 4 inches wide and tall, to create the Buschmann Aura about 1820. This blow-only design allowed tunes to be played and became somewhat popular in Germany and Austria, but was a rather limited instrument due to its size and design. The next version of the modern harmonica came in America from a Bohemian immigrant known today only by his last name, Richter. He created a 10-hole, diatonic harmonica called the "Vamper" with two stacked reed plates that would produce a consistent tone when blowing or drawing air over the reeds. Its size, approximate 4 inches wide but only 1 inch tall, made it an immediate improvement over its predecessors. Still, the modern harmonica was more a curiosity than a respected instrument.

It took a German clock maker to catapult the harmonica to its current status. Mathias Hohner had manufactured "mouth organs" in his spare time since the early 1850's. In 1865, he sent a small supply of his harmonicas to his cousins, who had emigrated to America a few years earlier, with the intent of establishing a market for his product. The tone and beauty of these simple instruments quickly won over many Americans, despite the looks of puzzlement these "immigrant salesmen" were likely given as they introduced their wares. Its portable size, quality construction, and superb tone made harmonicas a quick addition to the American landscape. Hohner almost singe-handedly established the harmonica in the American musical lexicon.

Harmonicas have a simple construction. The cover plate is the outer shell of the instrument. Its primary purpose is to hold the other parts of the harmonica together. The body or comb of the instrument provides the holes to blow or draw air. The reed plates sit on top and below the comb. In a standard diatonic harmonica, there are two reeds for each hole-- one used on draw notes and the other on blow notes.

Materials used for the comb of the harmonica have their own tonal characteristics and unique quality. Wood typically produces a resonant, full-bodied timbre with an even note reproduction from lows to highs. A plastic comb is characterized by a warm, even sound while being smooth on the lips. Also available are metal bodies or a metallic finish which produce a bright and clear sound.

The pitch and resultant scale of the harmonica is directly related to two factors; the material that the reeds are made of and the length of the reed. Metal is the most common material used for reeds in instrument quality harmonicas. Plastic may be used as well but is most commonly found in inexpensive toys. The length of the reed determines the pitch; that is, the longer the reed, the deeper the pitch.