"Firth of Fifth" is a song by the British progressive rock band Genesis. It first appeared as the third track on the 1973 album Selling England by the Pound, and was performed as a live piece either in whole or in part throughout the band's career.

Genesis were an English rock band formed at Charterhouse School, Godalming, Surrey, in 1967. The band's longest-existing and most commercially successful line-up consisted of keyboardist Tony Banks, bassist/guitarist Mike Rutherford and drummer/singer Phil Collins. In the 1970s, during which the band also included singer Peter Gabriel and guitarist Steve Hackett, Genesis were among the pioneers of progressive rock.