Witness is the fifth studio album by American singer Katy Perry. It was released on June 9, 2017, by Capitol Records. For the album, Perry worked with numerous producers, including Jeff Bhasker, Mark Crew, Duke Dumont, Jack Garratt, Oscar Holter, Illangelo, Ilya, Max Martin, Ali Payami and Shellback. The album features guest appearances from Nicki Minaj, Skip Marley, and the Migos. Witness is an electropop album that delves into dance-pop and EDM genres, with lyrics on self-empowerment and feminism. Perry described it as an album of "liberation" and "purposeful pop".

Five singles aided Witness, out of which, three were released before the album and one reached the top-ten of the Billboard Hot 100 chart: the lead single, "Chained to the Rhythm" featuring Skip Marley, peaked at number four on the Hot 100. "Bon Appétit" featuring Migos peaked at number 59, while "Swish Swish" featuring Nicki Minaj reached number 46. "Save as Draft" and "Hey Hey Hey" were released as subsequent singles on June 26, 2017 and January 12, 2018, respectively, with "Hey Hey Hey" receiving a music video. To support the album's release, Perry broadcast herself on a four-day YouTube live-stream, titled Katy Perry Live: Witness World Wide.

Upon release, critics were divided towards the album. Some criticized the production and lyricism, while others welcomed the album's personal nature and singled out certain tracks for praise. Moving 180,000 album equivalent units in its first-week, Witness debuted atop the US Billboard 200 chart, becoming Perry's third chart-topping album in the country. The album also topped the charts in Canada and Spain, while reaching the top five in Belgium (Wallonia), the Czech Republic, Finland, France, Greece, Ireland, New Zealand, Norway, and Slovakia. It has sold 1.25 million copies worldwide and received Platinum or higher certifications in Canada, India, Mexico, Norway, and Poland.

To promote the album, Perry embarked on her fourth concert tour, Witness: The Tour, during 2017 and 2018. Prior to the release of the album, Perry had not released new material in four years, with the exception of the 2016 Summer Olympics anthem, "Rise". After releasing Prism (2013) and touring in 2014–2015, Perry went on hiatus to protect her mental health and to return afresh. Perry decided to shed her on-stage persona and embrace her self-proclaimed authentic self as Katheryn Hudson, her real name. As a result, she retired her long, dark hair for a short pixie cut, and adopted her natural blonde hair color.

Following the release of her fourth album Prism in 2013 and the end of the Prismatic World Tour in October 2015, Katy Perry told The New York Times in February 2016 that she was in the "research and development phase" of a new album. She decided to take a hiatus after the tour concluded to "give my mental health a break" before starting to write new songs the following June. Perry felt "refreshed" after the hiatus, and had over 40 tracks "in progress" before the year ended, changing her hair color to blonde short hair from her long black hair in the past. In August, the singer stated that she aspired to make material "that connects and relates and inspires" and told Ryan Seacrest that she was "not rushing" her fifth album, adding: "I'm just having a lot of fun, but experimenting and trying different producers, and different collaborators, and different styles." The album marked a departure from long time producer and co-writer Dr. Luke. In February 2017, Perry stated that the album was "definitely a new era for me" and "an era of purposeful pop" she was proud of. Later that month, she told Capital FM that "I've got something swirling, but I think I want to put out some songs first before I give them the full meal." The following May, Perry revealed to Entertainment Weekly that the album would include 15 of the 40 songs she wrote for it, and described the record as "fun and dance-y and dark and light."

The album was partially inspired by Hillary Clinton's loss in the 2016 United States presidential election. Perry, a vocal supporter of Clinton, claimed "I was definitely not okay [after the election]. I couldn't write a happy-go-lucky song. I wasn't in that place but I also don't want to preach to people because I'm not that person either. I want to empower people and lift people up." Perry had previously performed at Clinton's 2016 presidential campaign in Philadelphia.^{[citation needed]}

Witness is an electropop album, containing influences of dance and EDM. As analyzed by Annie Zaleski from The A.V. Club, hooks are in short supply, replaced by grooves and atmosphere that pick and choose elements from 1990s house music, mainstream EDM, electro-tinged hip-hop, and 1980s new wave.

Witness opens with the title track, an electronic song backed by a 1990s house piano. "Hey Hey Hey" asserts that women can be complex people with a multitude of personality traits, as noted by Annie Zaleski from The A.V. Club, "Hey Hey Hey" depicts a narrow version of femininity and success and it perpetuates irksome stereotypes about strong women. "Roulette" is an EDM song described as "explosive" by Christopher R. Weingarten from Rolling Stone. "Swish Swish" runs throughout a house-influenced beat and contains a sample from "Star 69" by Fatboy Slim which itself samples "I Get Deep" by Roland Clark. "Déjà Vu" is "an electro-R&B ballad about wanting to free oneself from a dead-end relationship." "Power" explores a theme of self empowerment, Jillian Males from Pitchfork noted that the song "approximates feminism by politicizing a personal struggle for control."