A musical ensemble, also known as a music group or musical group, is a group of people who perform instrumental or vocal music, with the ensemble typically known by a distinct name. Some music ensembles consist solely of instruments, such as the jazz quartet or the orchestra. Some music ensembles consist solely of singers, such as choirs and doo wop groups. In both popular music and classical music, there are ensembles in which both instrumentalists and singers perform, such as the rock band or the Baroque chamber group for basso continuo (harpsichord and cello) and one or more singers.

Five-piece bands have existed in rock music since the development of the genre. The Beach Boys, The Rolling Stones (until 1993), Aerosmith, Def Leppard, AC/DC, Oasis, Pearl Jam, Guns N' Roses, Radiohead, The Strokes, The Yardbirds, 311 and The Hives are examples of the common vocalist, lead guitar, rhythm guitar, bass, and drums lineup whilst other bands such as Judas Priest have two guitarists who equally share lead and rhythm parts. An alternative to the five-member lineup replaces the rhythm guitarist with a keyboard-synthesizer player (examples being the bands Journey, Elbow, Dream Theater, Genesis, Jethro Tull, The Zombies, The Animals, Bon Jovi, Yes, Fleetwood Mac, Marilyn Manson and Deep Purple, all of which consist of a vocalist, guitarist, bassist, keyboardist, and a drummer) or with a turntablist such as Deftones, Hed PE, Incubus or Limp Bizkit.  Alternatives include a keyboardist, guitarist, drummer, bassist, and saxophonist, such as The Sonics, The Dave Clark 5, and Sam the Sham and the Pharaohs. Another alternative is three guitarists, a bassist and a drummer, such as Foo Fighters, Radiohead, and The Byrds. Some five-person bands feature two guitarists, a keyboardist, a bassist and a drummer, with one or more of these musicians (typically one of the guitarists) handling lead vocals on top of their instrument (examples being Children of Bodom, Styx, Sturm und Drang, Relient K, Ensiferum and the current line up of Status Quo). In some cases, typically in cover bands, one musician plays either rhythm guitar or keyboards, depending on the song (one notable band being Firewind, with Bob Katsionis handling this particular role).  Other times, the vocalist will bring another musical "voice" to the table, most commonly a harmonica or percussion; Mick Jagger, for example, played harmonica and percussion instruments like maracas and tambourine whilst singing at the same time. Keith Relf of the Yardbirds played harmonica frequently, though not often while also singing. Ozzy Osbourne was also known to play the harmonica on some occasions (i.e. "The Wizard" by Black Sabbath). Vocalist Robert Brown of lesser known steampunk band Abney Park plays harmonica, accordion, and darbuka in addition to mandolin. Flutes are also commonly used by vocalists, most notably Ian Anderson of Jethro Tull and Ray Thomas of the Moody Blues, though these are difficult to play while singing at the same time.  A less common lineup is to have lead vocals, two guitarists of varying types and two drummers, e.g. Adam and the Ants.

are there some bands which have musicians singing and playing an instrument at the same time?
singing. Ozzy Osbourne