"It's a Sin" is a song by English synth-pop duo Pet Shop Boys from their second studio album, Actually (1987). Written by Chris Lowe and Neil Tennant, the song was released on 15 June 1987 as the album's lead single. It became the duo's second number-one single on the UK Singles Chart, spending three weeks atop the chart. Additionally, the single topped the charts in Austria, Denmark, Finland, Germany, Ireland, Norway, Portugal, Spain, Sweden and Switzerland, while reaching number nine on the US Billboard Hot 100.

A demo of the track was first cut in 1984 with Bobby Orlando, and the song's form in the demo remained intact to the final version, although the released production is far more dramatic.