A cappella music is vocal music or singing without instrumental accompaniment, or a piece intended to be performed in this way. A cappella is latin for like the chapel (music); the term is due to restrictions on the use of instruments in medieval churches. It is often spelled as a capella, or acappella, though a cappella is historically more correct.

A cappella music was and is often used in church music. Gregorian chant is an example of a cappella singing, as is the majority of sacred vocal music from the Renaissance. The Madrigal, up until its development in the early Baroque into an instrumentally-accompanied form, is also usually an a cappella form. The Amish, Old Regular Baptists, Primitive Baptists, most congregations of the Church of Christ, and the Old German Baptist Brethren, as well as some Presbyterian churches devoted to exclusive Psalmody, are religious bodies known for conducting their worship services without musical accompaniment. Eastern Orthodox Christians (especially Russian and other Slavic groups) insist on singing unaccompanied by instruments. Sacred Harp, a type of religious "folk" music, is an a cappella style of religious singing. It is more often sung at singing conventions than at church services.

Many standard choral works are a cappella in that no accompaniment is written in except perhaps for rehearsal purposes. But in the modern parlance, it applies to vocal performers who disdain instrumental accompaniment in all cases. A cappella music attained renewed prominence in the 1980s and 1990s, spurred by the success of songs by popular recording artists such as Bobby McFerrin, Die Prinzen, Rockapella and Boyz II Men. Barbershop, doo wop, and contemporary a cappella are some of the major movements within modern a cappella music-making.

Arrangements of popular music for small a cappella ensembles usually include one voice singing the lead melody, one singing a rhythmic bass line, and the remaining voices contributing chordal accompaniment (In Japan, these parts are known as vocal, bass, and chorus, respectively). However, many contemporary a cappella groups have adopted other approaches, including polyphonic treatments and "human beatbox" effects. A cappella can also describe the practice of using just the vocal track(s) from a multitrack recording to either remix or put onto vinyl records for DJ's.

A popular movement in American colleges and universities is the presence of collegiate a cappella.

A cappella ensembles

• Acappella
• A Cappella Harmony Quartet (AHQ)
• Ac Rock website
• The Acabelles of Florida State University website
• All-Night Yahtzee of Florida State University website
• The Anita Kerr Singers
• Anonymous 4
• AVB
• Bella Voce
• The Birmingham Sunlights
• The Bobs
• Boyz Nite Out website
• The Brown Derbies of Brown University
• The Connecticut College Co Co Beaux
• The Comedian Harmonists
• Chord on Blues
• The Cornell Hangovers website
• Dale Warland Singers
• Da Vinci's Notebook
• DeCadence of University of California, Berkeley website
• The EDLOS
• The Flying Pickets
• Georgetown Phantoms of Georgetown University website
• Georgetown University Chamber Singers website
• Glad
• Impulse
• The King's Singers
• Ladysmith Black Mambazo
• Last Call of Cornell University
• The MadHatters of the University of Wisconsin-Madison website
• Neri Per Caso
• On a Sensual Note of American University
• Penn Masala
• The Princeton Roaring 20 website
• Rajaton
• The Real Group
• Rice Philharmonics website
• RIT Brick City Singers
• Rockapella
• Solfa
• St. Olaf Choir
• Street Sounds
• Sweet Honey in the Rock
• The Swingle Singers
• Take 6
• Take Note website
• Toxic Audio
• TR Griffin website
• Try Tone (Japanese)
• The University of Rochester YellowJackets website
• The Vocal Majority
• Vox One
• The Williams Octet
• Wise Guys
• The Yale Society of Orpheus & Bacchus
• The Yale Spizzwinks(?)
• The Yale Whiffenpoofs