A Fever You Can't Sweat Out is the debut studio album by American pop rock band Panic! at the Disco. Produced by Matt Squire, the album was released on September 27, 2005, through Decaydance and Fueled by Ramen. The group formed in Las Vegas in 2004 and began posting demos online, which caught the attention of Fall Out Boy bassist Pete Wentz. Wentz signed the group to his own imprint label, Decaydance, without them having ever performed live. It is the only album released during original bassist Brent Wilson's time in the band, but the exact nature of his involvement in the writing and recording process became a source of contention upon his dismissal from the group in mid-2006.

The album was recorded on a small budget at SOMD! Studios in College Park, Maryland over several weeks in June 2005. The group had only graduated from high school one month before. With lyrics written by lead guitarist and backing vocalist Ryan Ross, the album is divided into halves stylistically; the first half is primarily pop-punk with elements of electronic music, while the second half employs more traditional instrumentation, with influences of baroque pop.

Upon its release, A Fever You Can't Sweat Out became a commercial success. Its second single, "I Write Sins Not Tragedies", peaked at No. 7 on the Billboard Hot 100. It helped bolster the album’s sales to 1.8 million in the US by 2011, making it the group's best-selling release. Despite its sales, the album polarized music critics, with many praising the album's catchiness and others criticizing its perceived lack of creativity. The band promoted the record with stints on the Nintendo Fusion Tour before its first headlining tour, the Nothing Rhymes with Circus Tour. In late 2015, it received an RIAA double platinum certification for 2 million US shipments. It then received a triple platinum certification in March 2019.