Hot n Cold

"Hot n Cold" is a song by American singer Katy Perry from her second studio album, One of the Boys (2008). She and Max Martin co-wrote the song with its producer Dr. Luke, with additional production from Benny Blanco. The track was released as the album's second single on September 9, 2008, and was the first single to be released after the album. "Hot n Cold" is primarily a pop and dance-pop record and its lyrics address an unstable romantic relationship caused by a partner's mood swings.

"Hot n Cold" charted at number one in Austria, Belgium, Canada, Chile, the Czech Republic, Denmark, Finland, Germany, Hungary, the Netherlands, Norway, Poland, Romania, Slovakia, and Switzerland as well as the top five in Australia, Bulgaria, Iceland, Ireland, Israel, New Zealand, Sweden, the United Kingdom, and the United States. It additionally was certified diamond in Brazil and Australia and multi-platinum in Canada, Denmark, New Zealand, Norway, the United Kingdom, and the United States. "Hot n Cold" is one of eight songs by Perry to sell over 4 million digital copies in the US, the others being "I Kissed a Girl", "California Gurls", "Teenage Dream", "Firework", "E.T.", "Dark Horse" and "Roar".

To promote "Hot n Cold", Perry marked the song's live debut with a performance on NBC's Today. She also performed the song at the 2008 MTV Europe Music Awards. The song's music video, which was directed by Alan Ferguson, was released on October 1, 2008, and features Perry as a bride who is about to marry her fiancé, who experiences a daydream in which she pursues him after he flees from the wedding. "Hot n Cold" was nominated for the Grammy Award for Best Female Pop Vocal Performance at the 52nd Annual Grammy Awards. Perry has also performed the song on the Hello Katy Tour, the California Dreams Tour, the Prismatic World Tour, and Witness: The Tour.

The song has been included in games such as The Sims 2: Apartment Life and the first Just Dance, and shows such as MasterChef Australia and RuPaul's Drag Race Down Under, alongside Perry's concert film The Prismatic World Tour Live. A parody of the song was planned to appear in Sesame Street, but the segment was left unaired due to controversy relating to Perry's cleavage, although it still released on Perry's YouTube channel before the controversy. The incident would later be parodied by Perry herself on Saturday Night Live, where she also appeared as a musical guest.