Spears began writing songs for In the Zone while touring around the world, despite not knowing the direction of the album. She started to experiment with different producers, trying to find those who she had chemistry with. The first song recorded was "Touch of My Hand", which Spears claims set the mood for the album. She co-wrote several tracks, and often changed the lyrics to suit herself. Spears stated she was an autobiographical songwriter, although not the point were she felt self-exploited. She also explained that the sexual nature of In the Zone was subconscious and happened while she was in the process of developing the album. The topic for the songs range from love, dancing, empowerment, and in the case of songs such as "Touch of My Hand", sex and masturbation.
After its release, In the Zone received mixed reviews from critics. Some appreciated the album, calling it a strong and confident pop record, while complimenting the mix of different styles and Spears's skills as a songwriter. Others however, criticized it for what they perceived as distant and processed vocals. Commercially, In the Zone became an international success, debuting atop of the charts in France and the United States, and peaking inside the top ten in eleven countries. In the United States, she became the first female artist to have four consecutive number-one albums. In the Zone went on to become the eighth best selling album of 2003.
Four singles were released from the album: "Me Against the Music", "Toxic" and "Everytime" became worldwide hits, peaking at number one in Australia and reaching top five positions worldwide. To promote In the Zone, Spears performed the songs in a number of television appearances and also embarked on The Onyx Hotel Tour. The album and its music videos are largely seen by critics as the end of her transition from teen pop star to a more adult female artist. In 2009, Amy Schriefer of NPR listed In the Zone as one of The 50 Most Important Recordings of the Decade, calling it "a primer on the sound of pop in the '00s".