"4 Walls" is a song recorded by South Korean girl group f(x) for their fourth studio album of the same title. The song was written by Jam Factory's Lee Seu-ran, whilst production was handled by LDN Noise, Tay Jasper, and Adrian McKinnon. It was released on October 27, 2015 as the lead single in conjunction with the release of the album through SM Entertainment, and marked the group's first single since the departure of Sulli in 2015. Musically, "4 Walls" is described as a dance-oriented tropical house song, incorporating stylistic elements from UK garage and deep house. It was released as the group's second double A-side CD single in Japan with a new track "Cowboy" on November 2, 2016.