There are (at least) three bands with this name: a Canadian classic rock band; a Swedish punk band; and a Medieval/Folk band from Tasmania.

Canadian rock band: Harlequin was a Canadian rock band that formed in Winnipeg in 1975 and lasted until the mid-1980s.

The original members of Harlequin were vocalist George Belanger, guitarist Glen Willows, keyboard player Gary Golden, drummer David Budzak and bassist Ralph James. Harlequin signed with Epic Records in 1979 and had a string of hit singles in Canada. Their biggest hit single is "Innocence" which topped Canada's charts.

Belanger has since reformed the band, again in Winnipeg. Their latest release is Waking the Jester [2007]. Ralph James is still very active in business side of music, managing The Agency, a large music booking firm.

The Swedish Harlequin was active between 1992 and 1998 in Mariestad, Sweden.(2)

The Tasmanian band is currently active, and becoming well known in folk and re-enactment circles in Australia. To quote the notes on their 2005 album "La Vielle": Harlequin's music has been resurrected from & inspired by mediaeval, middle eastern & eastern european traditions and is played on mediaeval instruments handcrafted by the members.