The song reached number one on the UK Singles Chart for three weeks in 1987.
"It's a Sin" was the lead single from the duo's second studio album, Actually.
It became the duo's second UK number one single.
The song is a description of Tennant's Catholic upbringing and education at St Cuthbert's High School in Newcastle upon Tyne, implying that everything that is perceived to be pleasurable in life is regarded as sinful.
The song uses extensive samples from Latin masses (specifically, Tennant reciting a part of the Confiteor, and other sounds recorded at locations such as Westminster Cathedral) and religious imagery throughout to reinforce the feel of the song.