What a Girl Wants

Shelly Peiken wrote "What a Girl Wants" with Guy Roche, drawing on her relationship with her husband. The pair worked with a cassette tape one day, experimenting with vocals and hooks, and Peiken decided the work-in-progress had potential and would return to it later. She said the song and "Bitch", another of her co-writes, had a common thread because they came from the same soul. Originally titled "What a Girl Needs", the song was recorded in 1998 by French singer Ophélie Winter, who adapted French lyrics for it on her album Privacy, where it appeared in both languages as "Ce Que Je Suis". Peiken and Roche then pitched the song to RCA Records, and after the title changed it was recorded by Christina Aguilera for her 1999 debut album.

It was the first track recorded for the album, in June 1998. After the success of "Genie in a Bottle", the label called for a second recording, made in September 1999, which changed the original key and edited rhythmic changes. This re-recorded version went to contemporary hit radio in the United States on November 8 and was released internationally instead of the original, which had come out in Japan earlier that year.

The single became Aguilera's second consecutive US Billboard Hot 100 number one and the first of the 2000s, also topping charts in Brazil, Canada, New Zealand, and Spain. Nominated for Best Female Pop Vocal Performance at the 43rd Grammy Awards, it was later reworked in Spanish as "Una Mujer" for Mi Reflejo (2000). Aguilera performed it on tours through 2019, including the Back to Basics Tour and The X Tour.