"Peek-a-Boo" (Korean: 피카부; RR: Pikabu) is a song recorded by South Korean girl group Red Velvet for their second studio album, Perfect Velvet (2017). An up-tempo dance-pop track with tropical house elements, it was written by Kenzie, Ellen Berg Tollbom, Cazzi Opeia, and duo Moonshine, while production was handled by the latter contributor. The song was released in conjunction with its parental album on November 17, 2017, through SM Entertainment. It was later re-recorded in Japanese for the group's second Japanese extended play Sappy, which was released on May 29, 2019. "Peek-a-Boo" received generally positive reviews from critics, who noted the group's transition from a brighter and bubblier image from their last two singles "Rookie" and "Red Flavor" to a more mature sound. To promote the single, Red Velvet held a comeback showcase on the day of its release and promoted the song on several music programs in South Korea. The group additionally performed it on several year-end music award ceremonies, along with "Red Flavor".