The Dream Within a Dream Tour was the fourth concert tour by American entertainer Britney Spears. It was launched in support of her third studio album, Britney (2001). The tour was promoted by Concerts West, marking the first time Spears did not tour with Clear Channel Entertainment. On September 21, 2001, a North American tour was announced that kicked off in November after various dates were postponed. In February 2002, Spears announced a second leg of the tour. It was directed and choreographed by Wade Robson, who explained the main theme of the show was Spears's coming of age and newfound independence. The stage was designed by Steve Cohen and Rob Brenner and was composed of a main stage and a B-stage, united by a runway. Inspired by Cleopatra's barge, a flying device was developed so Spears could travel over the audience to the B-stage. The setlist was mostly composed by songs from the supporting album, as Spears felt they were more reflective of her personality. Songs from her previous two studio albums were also included in remixed form by Robson.

The show was divided into seven segments with the last one being the encore. Spears opened the show hanging from a gyrating wheel; it continued with Spears performing a medley of older hits, jumping in bungee cords from the flying device onto the stage and dancing in a jungle setting. Most of the performances were accompanied by extravagant special effects, including confetti, pyrotechnics, laser lights, and artificial fog and snow. In the encore, there was a water screen that pumped two tons of water into the stage; this was considered one of the signature performances of the tour. During the 2002 leg, some changes were made; several songs were remixed, and Spears premiered various unreleased songs which included "Mystic Man". The show received acclaim from critics, who praised the show for being innovative and entertaining, while some dismissed it for taking the attention away from the music.

According to Billboard, the 2001–02 dates in North America had an average of $803,683 in gross and 14,344 in attendance. Pollstar stated that the tour had a total gross of $53.3 million and 946,169 tickets sold in 66 of 69 shows. On April 25, 2002, Spears performed at a Japanese sold-out show at Tokyo Dome in Tokyo for 62,011 fans, grossing $2,921,302. On July 27, 2002, Spears performed for 51,261 fans at Foro Sol stadium in Mexico City. The show grossed $2,251,379 and was the 37th on Pollstar's Top 200 Concert Grosses in North America. During the second show in Mexico, Spears left the stage after the sixth song due to a lightning storm; the show was canceled and angered the audience. The tour was broadcast live on an HBO special on November 18, 2001, and went on to win an Emmy for Outstanding Technical Direction on the 2002 ceremony. A DVD titled Britney Spears Live from Las Vegas was released in January 2002. In Spears' 2023 memoir The Woman in Me, she names the Dream Within a Dream Tour as her favorite tour of her entire career.

On July 19, 2001, Spears's band announced there would be a tour to support her third studio album, Britney (2001). The following day, Spears's label Jive Records confirmed that there was a tour planned for the fall. The Dream Within a Dream Tour was promoted by Concerts West, chosen after a much publicized battle with concert promoter Clear Channel Entertainment (CCE), who had handled her previous concert tours. It marked the first time Concerts West outbid CCE, with reports claiming Spears would earn between $13 and $15 million during the tour. Spears's manager Larry Rudolph commented on the situation, saying,

"Clear Channel is an incredible company, and I'm sure we'll be doing more business with them. We went with Concerts West because they're a strong touring company and because they have ancillary properties, in that [parent AEG owns] arenas and some 7,000 movie theaters throughout the country. This decision was not made to exclude Clear Channel. It was made to include Concerts West. [AEG] has the ability to help us market our core products—the album and tour—and our secondary properties—the movie— in ways that tipped the scale for us."

On September 20, 2001, dates were released along with the track listing of the album. The tour was slated to begin on October 26, 2001, but the opening of the show was pushed back until October 31 after Spears became ill and was prescribed five days of rest. The tour was postponed one more day due to production delays and finally kicked off at Nationwide Arena in Columbus, Ohio. Before the tour began, Spears announced she planned to give $1 of each ticket to the children of firefighters and police officers killed during the September 11 attacks. She also planned to sell merchandise and auction front row seats, hoping to raise $2 million. On February 26, 2002, more North American dates were released through her official website to kick off in Las Vegas at Mandalay Bay. The second leg of the tour was sponsored by Samsung. In conjunction with entertainment company WFX, they offered a cell-phone service that featured collectible merchandise and a membership card with access to backstage reports directly from Spears. She stated that "[the offering] is an exciting new way for me to stay connected with my fans".

The name of the tour was based on Edgar Allan Poe's poem of the same name. The tour was directed and choreographed by Australian choreographer Wade Robson. He explained the concept of the tour, saying,

"The show is gonna be really, really theatrical—it's really complicated. It's a massive show with a lot of new music. It's just gonna be really different. [...] You're gonna learn a lot more about her as a person. The show is gonna be really about how she's becoming a woman, how she's finding herself and her independence. She knows what she wants to do, she knows who she wants to be, and that's what the show's about."