"Sweet Little Mystery" is a song by Scottish soft rock band Wet Wet Wet. It is the fifth single from the band's debut album Popped In Souled Out (1987), released on Phonogram Inc. Records. The success of the song drove it to number five on the weekly UK Singles Chart the same year as its release. The following year, the song became an international hit, entering the top 20 in Belgium, France, Ireland, Netherlands and New Zealand. Its peak positioning in numerous weekly charts around the globe marked its contributions to the soft-rock genre which dominated the era.
"Sweet Little Mystery" is Wet Wet Wet's second biggest hit globally, with their cover of the Troggs' "Love Is All Around" being their most known song. The song endured widespread criticism and the group was later sued for copyright infringement by Van Morrison. The group received further criticism for similarities to John Martyn's "Sweet Little Mystery" (1980). Both John Martyn and Van Morrison received co-writers' credits for the song.
Five years after the band's split in 1997, Marti Pellow recorded the song solo in his 2002 album Marti Pellow Sings the Hits of Wet Wet Wet & Smile.