Britney

Her next album, Britney, was released on November 6, 2001, and debuted at number one in the charts, selling over 740,000 units its first week. This made her the only female artist in SoundScan history to have her first three albums debut at #1. The first single "I'm A Slave 4 U" was produced by The Neptunes, and its R'n'B stylings heralded the starlet's attempt to grow with her audience, young and old. Over 4 million copies of Britney were sold in the United States alone, and the album went on to sell over 12 million copies worldwide. While the album was very much a hit by anyone else's standards, these figures are low in comparison to the sales of her other albums.

Throughout 2001 and 2002, Spears took home such awards as Best-Selling Female Pop Artist and Best-Selling Female Dance Artist at the World Music Awards, Favorite Female Singer at the Nickelodeon Kids' Choice Awards, Choice Female Artist (in both 2001 and 2002), as well as Choice Hottie Female at the Teen Choice Awards and Best Female Artist at the MTV Asia Awards.

In 2002, Spears starred in a movie, Crossroads, which reached number two in the box office charts. Songs from the album Britney appeared in the film. Spears' performance was poorly received by critics, and she netted herself a Razzie Award for Worst Actress of 2002, tied with Madonna. One of the tracks off of Britney, "I'm Not A Girl, Not Yet A Woman," also 'won' for Worst Original Song. This wouldn't be her last encounter with the awards show, however; in 2005, she was proclaimed Worst Supporting Actress for her cameo role in the documentary Farenheit 9/11. In June 2002, Spears branched out as a restaurateur with the opening of a New York City eatery, NYLA; but the venture was not a success and the restaurant closed in 2003.

In September 2002, she took a break from the spotlight, and in 2003 many music industry critics speculated that her career was in decline. Over the course of her first three albums, Britney Spears had sold approximately 57 million copies worldwide.

In 2003, Spears was nominated for two Grammy awards yet again: Best Female Pop Vocal Performance for "Overprotected", and Best Pop Vocal Album for Britney. She did not win either award.

In the Zone

Her fourth album, In the Zone, was released on November 18, 2003. Jettisoning the Max Martin produced synth pop of her earlier releases, the album took in lesser-known producers such as RedZone as well as such big names as Moby and R. Kelly. Spears co-wrote eight of the album's thirteen songs. In the Zone rose straight to the top of the album charts in its debut week. Spears is the only female in music history to have her first four albums debut at No. 1. After an opening performance in which she kissed Madonna at the 2003 MTV Video Music Awards in August, Madonna was also featured on the album's first single, "Me Against the Music". The single only reached No. 35 on the Hot 100, but was a No. 1 hit in other countries. In the Zone, however, has sold close to 3 million copies in the United States alone and over 9 million copies worldwide.

On January 3, 2004, Spears married her childhood friend Jason Allen Alexander at The Little White Wedding Chapel on the Las Vegas Strip in Las Vegas, Nevada. The couple promptly arranged for an annulment, which was granted on January 5, ending their 55-hour marriage. Following the wedding, Spears released the second single from In the Zone, "Toxic", which became a worldwide hit and a No. 1 hit in over twenty different countries. The single occupied the No. 1 slot in the US for four consecutive weeks, though it only peaked at number 9 on the Billboard Hot 100 Singles Chart.

In March, Spears embarked on her fourth world tour, "The Onyx Hotel Tour", which grossed over $34 million dollars and was seen by over 600,000 fans in North America and Europe. Meanwhile, the album's third single, "Everytime", was starting to receive radio play. While the song only reached No. 15 on the US Billboard Hot 100 chart, it was a No. 1 hit overseas in such countries as the UK and Australia. In June, she cancelled the remaining dates of her tour after injuring her knee during the filming of a video for her fourth single, "Outrageous". Shortly after returning from hospital, Spears, 22, announced her engagement to dancer Kevin Federline, 26. Federline was formerly linked with actress Shar Jackson, with whom he has two children.

In September 2004, Forbes estimated Spears' net worth at $35 billion.

On the night of September 18, 2004, Spears married Federline before 20-30 guests in a private non-denominational ceremony at a residence in Studio City, California. Spears wore an off-white dress and Federline wore an off-white tuxedo. The men and women attending the ceremony wore light blue and pink sweatsuits respectively. The legitimacy of the marriage was initially questioned, but on November 18, 2004 a representative of the Los Angeles County registrar's office confirmed that Spears and Federline had successfully filed their marriage license with the county within ten days of their ceremony and were therefore legally married.

During 2004, Spears won for Choice Single ("Toxic") at the Teen Choice Awards, Best Female Act at the MTV Europe Music Awards and received the award for Hot Dance Sales Single of the Year ("Me Against the Music" featuring Madonna) at the Billboard Music Awards; Spears' public appearance at the ceremony on December 8, 2004 was her first since marriage to Federline.

In 2005, Spears received her first Grammy award for "Toxic" in the category of Best Dance Recording...