The album marked a departure for Simpson, who executive produced the record and shifted her sound in a more dance-pop direction.

Wanting to experiment with new sounds to make a “fun party album”, Simpson enlisted multiple producers including Timbaland, Jerome Harmon, Chad Hugo of The Neptunes, and Kenna.

Though the album did not achieve the commercial success of Autobiography or I Am Me, it has been lauded by critics for its eighties-infused electropop sound, which Simpson has admitted was “ahead of its time.”[4][5] In November 2006, after completing her run as Roxie Hart in the London production of the musical Chicago, Simpson said that she was going to meet with record executives soon to begin work on her third album.

[9] Though it was initially reported that Simpson was also working with The Cure frontman Robert Smith,[9] both parties later denied a collaboration.

Although Simpson said her sound would stay in the pop rock realm, she also mentioned that her music was evolving and would have less emphasis on relationship troubles and breakups.

[16] For Bittersweet World, Simpson worked with hit producers like Timbaland, King Logan of The Royal Court, Chad Hugo of The Neptunes, Kenna, Jack Joseph Puig, Jim Beanz, and J-Roc.

"Murder" originally featured a rap from Gym Class Heroes frontman Travie McCoy,[18] but he was replaced by Izza Kizza on the album version.

Simpson said she was inspired by women like Chrissie Hynde, Debbie Harry and Pat Benatar, because "they are strong and vulnerable simultaneously, yet they still make you want to dance.

[18] Rolling Stone noted "What I've Become" as an "excellent coming-of-age anthem" and "a paparazzi kiss-off with an appealingly honest chorus: 'I’ve just begun to find my way.

The song is a spare ballad that is “stripped down to piano, strings, and vocals,” with Simpson citing it as her favorite on the album.

[35] Though Bittersweet World's release was expected in March, its new date was revealed to be April 15 as Simpson did promotional radio interviews.

[19] The 13-city tour began in January 2008 at the Myst Club in Scottsdale, Arizona, and ended at Mansion in Miami Beach in March.

[41] Simpson also did promotion in Europe,[41] performing “Outta My Head” on The Paul O’Grady Show[42] and on BBC Sounds.

[43] Clothing retailer Wet Seal partnered with Simpson for a collection of tops designed by the singer to coincide with the album's release.

[49] Although the song received a positive reception from critics,[50] it became Simpson's first single to not make the Billboard Hot 100 chart.

[62] The song "Boys" was speculated to be the third single off the album, due to its promotion in ads and being performed by Simpson on Dancing With the Stars.

[24][70][71][72] In a three-star review, Rolling Stone said Simpson "skillfully shifts her crunchy, guitar-driven pop to eighties-influenced electro-rock with the help of Timbaland and the Neptunes' Chad Hugo.

"[29] Stephen Thomas Erlewine wrote, “Where Avril [Lavigne] beat a retreat to the bratty punk-pop that brought her fame, Ashlee has pulled a red hoodie over her head, amped up the dance beats, revved up the '80s retro fetish, and created something that feels of the 2008 moment.”[65] Entertainment Weekly gave the album a B grade, saying the album is filled with “polished hooks and pretty melodies" and has a "giddy neon energy.”[32] The New York Times and People magazine both selected Bittersweet World as a critic’s choice pick,[26][73] with the former saying the music “pays off in songs with crisp beats, teen-seeking choruses and cheerfully obvious lyrics", and that while the album “couldn’t be more calculated, that doesn’t prevent it from being catchy, too.”[33] Digital Spy said it was "easily the best album made by a Simpson sister".

[24][74][75] Jill Menze of Billboard praised the album's fun bubblegum sound, but also noted while Bittersweet World "is a party worth attending...not much is missed if your invite got lost in the mail.

[77][78][79] Elysa Gardner of USA Today called Bittersweet World "a collection of bouncy, banal homages to the '80s" and wrote Simpson, "aided by Timbaland, The Neptunes' Chad Hugo and others, channels Debbie Harry, Madonna and Toni Basil about as well as any girl who could afford the help.