Waking Up in Vegas

"Waking Up in Vegas" is a song by American singer Katy Perry, released as the fourth and final single from her second studio album, One of the Boys (2008). Perry wrote the song with Desmond Child and Andreas Carlsson, and Greg Wells produced it alongside Perry. Wells is also credited for playing all the instruments on the song. The song was recorded in Rocket Carousel, based in Los Angeles. "Waking Up in Vegas" is a pop rock and power pop track about an underage couple getting drunk and blowing their money in Las Vegas, paying homage to the phrase "what happens in Vegas, stays in Vegas."

The single was officially released to US radio stations on April 21, 2009, through Capitol Records. It attained commercial success, charting at number one in Hungary while reaching the top 10 in Canada, Ireland, New Zealand, Slovakia, and the United States as well as the top 20 in Australia, Iceland, Israel, the Netherlands, and the United Kingdom. "Waking Up in Vegas" also received multi-platinum certifications in Australia, Canada, and the United States.

The music video was directed by Joseph Kahn and it features Perry and American actor Joel David Moore in Las Vegas Valley partying and gambling. She performed the track during her Hello Katy Tour and California Dreams Tour, and an acoustic snippet was sung during the Las Vegas show of Witness: The Tour. The song was also used to promote Perry's concert residency at Resorts World Las Vegas, Play, which began in December 2021. A jazz version of the song was later included in the actual setlist itself.