Originally titled as "What Doesn't Kill You (Stronger)", the song served as the album's second single on January 17, 2012, through RCA Records.

Written by Kelly Clarkson, Jörgen Elofsson, Ali Tamposi, and David Gamson, with additional writing and production by Greg Kurstin, "Stronger (What Doesn't Kill You)" is an uptempo song that draws from the genres of dance-pop and electropop.

Its lyrical content mainly explores themes of empowerment and recovery following a heartbreak, with the chorus inspired by a Friedrich Nietzsche quotation: "That which does not kill us makes us stronger.

It held the number one position for three non-consecutive weeks, surpassing "A Moment Like This" (2002) and "My Life Would Suck Without You" (2009) as her longest-running number-one single on the chart.

Internationally, "Stronger" topped the national charts of Poland, Slovakia, and Slovenia and attained a top-ten position in over fifteen countries around the world, eventually selling over five million copies worldwide.

[2] In an interview with American Songwriter, Tamposi revealed that the song was inspired by the Friedrich Nietzsche adage ("That which does not kill us makes us stronger") that her mother told her as advice.

[2] Aldrich had then commissioned Greg Kurstin, whom Clarkson wanted to collaborate with, to produce and add additional writing to the final version.

[9] According to the sheet music published by Hal Leonard Corporation at Musicnotes.com, it is set in a common time and has a moderately fast tempo of 116 beats per minute.

[10] The song begins with a "rumbling guitar" and a "shimmering synth" riff as Clarkson sings the opening line "You know the bed feels warmer / Sleeping here alone.

"[7] Jason Lipshutz of Billboard noted that the guitar riff in the verses is reminiscent of Clarkson's "Since U Been Gone" which narrates an anthem of personal reinvention, and dancing.

"[15] After returning from a vacation on Tahiti, Clarkson found out over 50 of her newly recorded demo material were leaked online,[16] including "Stronger".

[18] In an attempt to counter-attack the leakage, RCA finally debuted the song online on October 5, 2011, three weeks ahead of the album's release.

"[24] Elizabeth Lancaster of MTV Newsroom listed it as one of five key tracks in Stronger, writing "Upbeat yet soulful, the chorus will drag you up and onto the floor to dance the heartache away alongside her.

"[26] Another positive reception came from Glenn Gamboa of Newsday, who praised Clarkson for "infusing her tales of empowerment after a breakup with her unique combo of vulnerability and sass.

"[27] Jonathan Keefe of Slant thought that the song is "tailor-made for radio play" and that "the chilly electro-pop that Greg Kurstin brings to the verses, suggests a top forty version of Robyn's "Call Your Girlfriend" (2010).

[28] Additionally, it also appeared at number two of Clarkson's Top 15 Biggest Billboard Hot 100 hits through the week ending April 29, 2017.

For a laugh, look up the YouTube video in which some wag mashed together a medley of 30 different songs that already borrowed "That which does not kill me makes me stronger" as a lyrical hook.

"[30] Kevin Ritchie from Now Magazine emphasized that the lyrics are "about as clichéd as a mission statement can get, but it also makes for a solid pop song.

"[32] In the United States, "Stronger" topped sixteen Billboard charts, marking career highs for Clarkson.

[33] Boosted by digital sales following the release of Stronger, the song debuted on the Billboard Hot 100 chart as an album cut at number 64 on the week ending October 30, 2011.

[35] Following its release as a single, "Stronger" re-entered Billboard Hot 100 at number 58 after Clarkson performed it on Saturday Night Live on the week ending January 21, 2012.

[73] In December 2012, Popjustice ranked "Stronger" at number 1 on their "Top 45 Singles of 2012" list, stating that "this song is timeless in its amazingness" and claiming that no one "but Kelly Clarkson who could have pulled off this tune.

[77] On November 21, 2011, Clarkson announced on her website that she wanted to incorporate a global flash mob into the accompanying music video of "Stronger".

Prior to its release, Jenna Halley Rubenstein of MTV Buzzworthy predicted that the video would depict women who triumphed over broken relationships as a homage to self-sufficiency.

[83] Leah Collins of The Vancouver Sun interpreted that the video depicts Clarkson developing a sense of strength and endurance as well as an ability to lead a large-scale dance routine after surviving a trauma.

[85] Rand Duren of The Dallas Morning News also reiterated that the music video is a reminiscent of "Since U Been Gone" and that it was great seeing more dancing and movement from Clarkson.

"[88] The same opinion was echoed by Robbie Daw of Idolator who thought the video was fun especially "when Kelly herself joins the giant mob at the very end."

[citation needed] Amber Riley, Naya Rivera, and Heather Morris performed the song in the season three episode of Glee, "On My Way", which aired on February 21, 2012.

[105][106] On April 11, 2012, it was covered by Hollie Cavanagh, Joshua Ledet and Jessica Sanchez in the eleventh season of American Idol.

[112] In 2018, Dove Cameron and China Anne McClain recorded a version with slightly altered lyrics for Disney's Descendants franchise.