Lost in the Sound of Separation is the sixth studio album by American rock band Underoath. It was released on September 2, 2008, through Solid State and Tooth & Nail Records. Following the release of their fifth studio album Define the Great Line (2006), relationships between members became strained to the point they almost broke up. They decided to go on a hiatus; Lost in the Sound of Separation was recorded at Glow in the Dark Studios in Atlanta, Georgia in March and April 2008. The band produced the album with Adam Dutkiewicz and Matt Goldman, both of whom worked on Define the Great Line. The album has been described as metalcore, post-hardcore and screamo, with elements of industrial, recalling the works of Refused, At the Drive-In, and Cult of Luna.

Underoath is an American rock band from Tampa, Florida. It was founded by lead vocalist Dallas Taylor and guitarist Luke Morton in 1997 in Ocala, Florida; subsequently, its additional members were from Tampa, including drummer, clean vocalist and last remaining core member Aaron Gillespie. The band's current lineup consists of Gillespie, keyboardist Christopher Dudley, lead guitarist Timothy McTague, bassist Grant Brandell, and lead vocalist Spencer Chamberlain. Originally, the band identified as a Christian group; they have since distanced themselves from Christianity.