"Womanizer" is a song by American recording artist Britney Spears from her sixth studio album Circus. It was released on September 26, 2008 by Jive Records as the first single of the album. The song, described by Spears as a girl anthem, recalls a womanizing man, while the protagonist of the song makes clear she knows who he really is. Produced and co-written by Nikesha Briscoe and Rafael Akinyemi of The Outsyders, the song is musically an uptempo electropop song with influences of Spears' songs from her previous two studios albums. Spears re-recorded some vocals after a snippet of the track was leaked before it was released.

The song was well-received by contemporary critics, with reviewers complimenting its hook and deeming it as a comeback single for Spears. "Womanizer" was commercially successful, topping the charts in Belgium, Canada, Turkey, Denmark, Finland, France, Norway, Sweden and the United States. It also reached the top ten in Australia, Japan, New Zealand and many European countries. In the United States, it was her first single to reach number one since "...Baby One More Time", almost 10 years prior.

The music video was directed by Joseph Kahn and was created by Spears as a sequel to the music video of "Toxic". The video portrays Spears as a woman who disguises herself in different costumes and follows her boyfriend through his daily activities to expose him in the end. The video also contains scenes of Spears naked in a steam room, as a response to the attacks she had received over the years about her weight. It received positive reviews and was considered as a return to form for Spears.

Spears performed "Womanizer" on various TV shows and on The Circus Starring Britney Spears, where she performed it as the encore number of the show, wearing a policewoman uniform. The song has been covered by a number of artists from different genres, including Lily Allen, Franz Ferdinand and Girls Aloud. It received a Grammy Nomination in 2010 in the Best Dance Recording category.

The song was written and co-produced by Nikesha Briscoe and Rafael Akinyemi of the production team, The Outsyders. Spears recorded main vocals with Brendan Dakora at Glenwood Place Studios in Burbank, California and Bojan "Genius" Dugic at Legacy Studios in New York City. ProTools engineering was done by John Hanes, assisted by Tim Roberts. On September 19, 2008, a low quality 37 second snippet of the song was posted on the official website of 107.5 The River, a radio station in Lebanon, Tennessee. According to Jive Records, a representative of the label played a rough mix of the song for people at the station, who recorded it and leaked it on the Internet. The snippet was later removed from the website. The song was scheduled to premiere on September 23, 2008, but the release was delayed when Spears went into the studio to re-record some vocals. The new recordings were done with Jim Beanz and Marcella "Ms. Lago" Araica. The song was finally mixed by Serban Ghenea at MixStar Studios in Virginia.

"Womanizer" was officially sent to radio stations on September 26, 2008. A few days later, Spears talked about it during a live interview with New York's Z100 on October 18, 2008, stating, "It's basically saying, 'We know what you're up to.' It's about guys cheating on girls, it's a girl anthem. That's why I like it".

"Womanizer" is an uptempo electropop song with dark synths that runs through a dance oriented beat. It has been compared to previous Spears' songs such as "Toxic" (2003) and "Ooh Ooh Baby" (2007). It is written in the verse–pre-chorus–chorus form. The track opens with its characteristical sirens. According to Ann Powers of the Los Angeles Times, Spears "quick-witted" vocals are similar to the style of the Andrew sisters. It was also noted by Daily Newswriter Jim Farber that Spears' delivery has a "tone of petulance". After the bridge, Spears sings the chorus one more time and the song ends while the beat drops and Spears sings the "you’re a womanizer, baby" hook. The song is composed in the key of C# minor with 139 beats per minute. The chord progression in the song is C#m-F#m-E-Eb-D. Lyrically, the song refers to a womanizing man. It has been suggested that the lyrics address Spears' ex-husband Kevin Federline.

Peter Robinson of The Observergave the song the maximum five stars referring to it as a "comeback single" and as having a "genius hook". He added that the song "[has] been called lazy, largely by misinformed people who also think that Kylie's 'la la la's would have been better with proper words". Popjustice compared it to "Some Girls" by Rachel Stevens and added "[The] track lays a really strong foundation for the fully-realised comeback that didn't quite happen last time and it's hard not to think of it as a late contender for single of the year. [...] It's literally quite good". Myrddin Gwynedd of The New Zealand Heraldsaid "it's got hit written all over it". On the week of November 24, 2008, the Derby Telegraphchose it as single of the week. In the album review, Nekesa Mumbi Moody of The Providence Journalsaid that along with "Shattered Glass", they were "[two] fun disco tracks".

USA Todaywriter Steve Jones named it one of the standout tracks of the album and commented that "she seems most at ease when she's playing the teasing tart". Talia Kraines of the BBC commented that Spears needed more songs like "Womanizer", saying "Britney 2.0 needs to be full of wild dancefloor driven moves". Simon Price of The Independentcommented the song borrows its electronic sound from Goldfrapp. Ann Powers of the Los Angeles Timescomplimented Spears' delivery and the lyrics, saying the song is "about the kind of girl power that's focused on besting one obnoxious man, is also vintage and contemporary at the same time – more feminism as individualism". Mike Newmark of PopMatters called the song " a meaty, high-voltage shuffler helmed by the Outsyders, who do an admirable job of recreating the chemistry of Spears and Danja on last year’s single 'Gimme More'". Rolling Stonepraised the song as an "electro-glam stomp" and went on to describe it as "head-boppingly hypnotic".

Bill Lamb of About.com thought that Spears was confident, but the song sounded "like a rather weak attempt to approach the attitude of Katy Perry in a classic Britney futuristic bubblegum pop context". He would later name "Womanizer" the third most annoying pop song of 2008. Jim Farber of the Daily Newssaid the pre-chorus was the most repetitive in a pop song since The Shaggs's "Gimmie Dat Ding". Jim Abbott of the Orlando Sentinelcalled it "basically an adult update of her teen-pop tease act". Ian Watson of Dotmusic wrote that Spears sounded "trapped on this single. Not trapped, as in desperate and distraught, but trapped as in literally frozen – like she's been placed into a robot on a production line and she has to sing these words, dance these steps, work it like this, until the spotlight snaps off and the factory's powered down for the night". The song has been nominated for a Grammy Award in the category of Best Dance Recording on December 2, 2009. Spears had previously won the category in the 2004 ceremony for her single "Toxic". However, it lost to Lady Gaga's "Poker Face". The song was also nominated for Best Track at the 2008 Virgin Media Music Awards, but it lost to Katy Perry's "I Kissed a Girl".

In the United States, the song entered the Hot 100 at number ninety-six on the issue dated October 8, 2008. The following week, the song jumped to number one breaking the records for largest jump to number one and largest jump to any position in the history of the chart, previously held by T.I.'s "Live Your Life" and Beyoncé and Shakira's "Beautiful Liar", respectively. The record was later broken by Kelly Clarkson's "My Life Would Suck Without You". It also garnered first-week download sales of 286,000, the biggest opening-week tally by a female artist since Nielsen SoundScan began tracking digital downloads in 2003, surpassing the record previously held by Mariah Carey's "Touch My Body". The record was broken on January 27, 2010 by Taylor Swift's "Today Was a Fairytale". "Womanizer" was Spears' first number one single since her debut "...Baby One More Time" in 1999. On the week of January 3, 2009, the song reached number one on the BillboardPop Songs and number six on Radio Songs.

As of July 2009, "Womanizer" was listed at number thirty-nine in the best selling digital songs of all time, with sales over 2,777,600. In Canada, the single topped the Canadian Hot 100 on October 18, 2008, and stayed in the position for five consecutive weeks. "Womanizer" entered the Australian charts on October 13, 2008 at number sixteen. Three weeks later, it peaked at number five. It shipped over 70,000 copies, earning a platinum certification by the Australian Recording Industry Association (ARIA). In New Zealand, the song peaked at number nine on October 27, 2008. The song was certified gold according to the Recording Industry Association of New Zealand (RIANZ), selling over 7,500 copies. The track debuted at number four in the United Kingdom on November 9, 2008 and reached its peak position of number three four weeks later. On January 16, 2009, it was certified silver by the British Phonographic Industry (BPI), with sales over 60,000 copies. The song reached the peak in a number of European countries, including Belgium (Flanders), Denmark, Finland, France, Norway and Sweden. It also reached the top ten in Austria, Belgium (Wallonia), Czech Republic, Italy, Spain and the Netherlands. In addition, the track became Spears' sixth European number-one single.

The music video was filmed on September 24 and September 25, 2008 in Los Angeles, California, directed by Joseph Kahn, who previously worked with Spears for the music videos of "Stronger" and "Toxic". According to Kahn, Spears pitched him her original concept, which included all the main elements used in the final version. Spears thought of the video as a sequel to "Toxic", as seen in her documentary Britney: For the Record, whereas Kahn approached it as "a 2008 answer" to the previous clip. He added that, "'Toxic' was a crystallization of her career at that time, [...] There are elements and moments of that I felt could [have been] improved. ['Womanizer'] is a bit more fashion-forward". About how the concept of the video related to their previous work, Kahn commented that "It's just a great girl fantasy. There are things she's really good at, like having a really natural knack for knowing what girls want. [...] It's a much more mature sound and much more mature lyrics, and she always has the greatest ideas. She's hyper-aware of pop culture". The costumes and looks for each of the different women were chosen by Spears and Kahn. The scenes in the sauna were suggested by Kahn, as a response to the attacks Spears received over the years about her weight. He stated, "I knew that the whole world would be watching, so I wanted something in there that stated, 'This is Britney, this is why you should respect her'". The set was cleared for two hours, leaving her and Kahn alone shooting the sequence. Kahn also decided to end the video with an image of Spears smiling, because "We just needed to tell everybody she's OK". A censored version of the music video premiered on October 10, 2008 on ABC's 20/20at the end of their show. The uncensored version premiered on MTV the same night.

The video begins with an opening caption that reads "Womanizer". During the introduction, Spears is naked and smiling at a sauna, while covering herself with her hands. These scenes are seen throughout the video. When the first verse begins, a blond Spears wearing a slip nightgown is making breakfast for her boyfriend as he gets ready for work. When he is at the office, he sees a new secretary, which is actually Spears in disguise wearing horn-rimmed glasses and a pencil skirt. She starts dancing in front of him and sings the chorus. She makes him follow her into the photocopier, where she photocopies her buttocks. On the back, we see an awkward-looking man, the same who appears in the plane scene on "Toxic". Then, Spears is disguised as a redhaired waitress in a restaurant. She dances around him with her dancers and plays with him over the kitchen counter. After this, her boyfriend is seen getting driven home by Spears, disguised as chauffeur. She starts to kiss him, driving the car with her heel until both get home. Once they get into the bedroom, Spears reveals that she was the three women he was "womanizing" all along. She then begins attacking her boyfriend. This is shown through Spears as her three alter egos, and then as the real version of herself. Spears throws a blanket over him and making the bed. The video ends with Spears smiling and the opening caption.

Margeaux Watson of Entertainment Weeklysaid the video "looks promising. [...] The dancing is stiff and minimal, a disappointment since her moves are her strong suit. But this is a welcome return to the Britney we love — gorgeous, gyrating, greased up, and gamely playing the vamp". OK!commented that "in addition to seeing Brit in three different sexy getups, the video [...] features an oiled-up Britney writhing around in nothing but a smile". Rolling Stonesaid the video was "a cross between 'Toxic' and The Office" and added, "she’s dancing [and] looking like the old Britney". Courtney Hazlett of msnbc.com claimed "When Spears isn’t shown naked and writhing in a steam room, she’s fired up". news.com.au stated that "Britney Spears is back to her old sexy self and she's not afraid to flaunt it". TV Guidewriter Adam Bryant said that "the music video features some of the most strategically placed hands in music-video history [...] [The] video is quite a return to form for the troubled pop star".

The music video for "Womanizer" became a worldwide success right after it premiered on the Internet, gaining seven million viewers in less than 48 hours. The music video was listed as the best video of 2008 in polls by MTV and Fuse TV. It won Music Video of the Year at the 2009 NRJ Music Awards. The video was also nominated for Best Pop Video and Video of the Year at the 2009 MTV Video Music Awards. It lost the latter category to Beyoncé's "Single Ladies", but won Best Pop Video.

The song was performed for the first time at the Bambi Awards in Germany, on November 27, 2008. For the performance Spears wore hot pants, fishnet stockings and a black top hat. The ensemble was compared to the costume Madonna wore during the first act of her Sticky & Sweet Tour. Spears was also presented with an award for Best International Popstar by Karl Lagerfeld, who said, "I admire you ... not just for your art, but for your energy. [You are] coming back not only as a phoenix but as a bird of paradise". The following night, Spears performed the song at Star Academy, with similar choreography and dance moves but wearing a red strapless dress. On November 30, 2008, Spears performed at The X Factor. The performance was watched by over thirteen million UK citizens, making it the most viewed episode in the show’s history. On December 2, 2008, she performed the song at Good Morning Americaalong with a performance of "Circus". On December 15, 2008, she performed at the Japanese music show Hey! Hey! Hey! Music Champ. The following day, she performed at NTV Best Artist 2008in a black and gold bra, hot pants and a white top hat. She also sported a fake tattooed heart in her cheek.

The song was a major part in The Circus Starring Britney Spears, as the encore of the show. After a video interlude of Spears's music videos set to "Break the Ice" ended, Spears appeared wearing a police officer uniform designed by Dean and Dan Caten, with black sunglasses, a hat with her trademark logo and sequined handcuffs. Her female dancers were also dressed as policewomen, while her male dancers were dressed as criminals. During the performance, she danced and flirted with the male dancers. At the end of the song, she returned to the main stage while her dancers surrounded her and a shower of sparks fell over them. She thanked the audience and bowed to each side of the arena. She left the stage with an instrumental version of "Circus" playing in the background. The performance was praised for being a standout number in the show.

"Womanizer" has been covered by many artists from a variety of music genres, as well as a great number of amateurs. Clark Collis of Entertainment Weeklyexplained that "the song has been covered by other artists with an enthusiasm only matched in recent times by musicians’ desire to remake Radiohead’s 'Creep' in their own image". On December 8, 2008, New Zealand singer Ladyhawke performed a cover at BBC Radio 1's Live Lounge. The song was covered by American band The All-American Rejects on the Yahoo! Music Pepsi Smash show in December 2008. It was performed in an acoustic version, in which the band members played percussions with beer bottles. The cover also included an excerpt from The Turtles's "Happy Together". British singer Lily Allen also covered the song, because "simple really, I love Britney and I love the song". Her cover was a stripped down version, that according to Nick Levine of Digital Spy, "might provoke those who reckon it doesn't have much of a chorus to revise their opinion". Allen also performed the song as the encore during her 2009 tour. French singer Sliimy cover was deemed as an "indie makeover". He would later be the opening act of the second Paris date at The Circus Starring Britney Spears. On January 13, 2009, English singer Ana Silvera covered the song during one of her London concerts. On April 6, 2009, Scottish band Franz Ferdinand also covered the song at Radio 1's Live Lounge. Lead singer Alex Kapranos claimed "It's been the best song out in the last few months". It was also covered regularly by them during their 2009 American spring tour. The song was performed live by UK girl group Girls Aloud during their Out of Control Tour, starting April 24, 2009. Their version was released on their 2009 live album Out of Control: Live from the O2. "Womanizer" was also covered by Fall Out Boy, among others.