"Thinking of You" is a song written and recorded by American singer Katy Perry from her second studio album, One of the Boys (2008). It was produced by Butch Walker, and released on January 12, 2009 as the album's third single. "Thinking of You" is a pop rock and soft rock power ballad. Lyrically, the song deals with a break-up in which Perry does not want to move on but has no choice, and feels nostalgic of a previous lover while in a relationship with another man. It is one of the three songs on the album that Perry wrote solely herself along "One of the Boys" and "Mannequin".

The song peaked at number 29 on the US Billboard Hot 100 chart, becoming the album's only single to fail to reach the Top 20 in the United States, and peaked at number 27 in the United Kingdom. There are two music videos released for the song. The first was released in 2007 and featured Perry in two different rooms, black and white, and was directed by a friend of hers. The second was the commercial release in 2008 which was set in the 1940s and featured Perry playing a woman who lost her lover, a soldier (played by Matt Dallas), in battle during World War II. Perry began playing the song during gigs as early as 2006, and performed the song on all of her concert tours: the Hello Katy Tour, the California Dreams Tour and The Prismatic World Tour.

The song was included in the international soundtrack to India, a Love Story, a Brazilian telenovela and becoming most successful in Brazil.

"Thinking of You" was written by Perry and produced by Butch Walker. Amateur video of Perry performing an entirely acoustic version at the Hotel Café in Los Angeles as early as 2006 is available on YouTube. The song is a pop ballad song and features acoustic instruments. The single was released on January 12, 2009, in the US, and in Australia a week later.

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