A harmonica, or mouth organ, is a free-reed wind instrument.

Harmonica may also refer to:

• Adagio and Rondo for glass harmonica, flute, oboe, viola and cello, composed in 1791 by Wolfgang Amadeus Mozart
• Concerto for Harmonica and Orchestra, composed 1954 by Malcolm Arnold

• Cambridge Harmonica Orchestra, formed in 1981 in Cambridge, Massachusetts
• Cappy Barra Harmonica Band, an American harmonica ensemble active circa 1935–1945
• The Harmonica Gentlemen, an American trio active after World War II
• King's College Harmonica Band, formed in 1951 in Hong Kong
• Morton Fraser's Harmonica Gang, a British comedy musical group active circa 1946–1980s

• Chromatic harmonica, a type of harmonica with a button-activated sliding bar
• Glass harmonica, or glass harmonium, a type of friction idiophone
• Richter-tuned harmonica, or blues harp, a common type of harmonica
• Tremolo harmonica, a type of harmonica with two reeds per note

• HarmonicaUK, UK-based, founded in 1935 as the National Harmonica League
• The Society for the Preservation and Advancement of the Harmonica, US-based, founded in 1962

• "Alvin's Harmonica", a 1959 single by Alvin and the Chipmunks
• Harmonica Solos, a 2013 album by George Winston
• "Hey Harmonica Man", a 1964 single by Stevie Wonder
• Man Bites Harmonica!, a 1958 album by Jean "Toots" Thielemans

• Asia Pacific Harmonica Festival, held bi-annually since 1996
• Harmonica concerto, a list of such compositions
• Harmonica techniques, a list of such techniques
• Magnus Harmonica Corporation, formed in 1944 in New Jersey as the International Plastic Harmonica Corporation

• Brenthia harmonica, found in the Philippines
• Didrimys harmonica, found in Sri Lanka, Java, Borneo, and New Guinea
• Glaucocharis harmonica, endemic to New Zealand

listed alphabetically by last name

• Terry "Harmonica" Bean (born 1961), American musician born in Mississippi
• Harmonica Fats (1927–2000), American musician born in Louisiana
• Harmonica Frank (1908–1984), American musician born in Mississippi
• Harmonica Hinds (born 1945), Trinidadian-American musician
• Harmonica Shah (born 1946), American musician born in California
• Harmonica Slim (1934–1984), American musician born in Texas
• George "Harmonica" Smith (1924–1983), American musician born in Arkansas

• Elementa harmonica, a treatise on the subject of musical scales by Aristoxenus from the 4th century BC
• Harmonica gun, a type of firearm
• Harmonica house, a type of row house in North Korea
• Harmonica Incident, an event during the New York Yankees' 1964 season
• Tunes for a Small Harmonica, a 1976 novel by Barbara Wersba

• All pages with titles containing Harmonica