"Stronger (What Doesn't Kill You)", sometimes referred to as just "Stronger", and originally known as "What Doesn't Kill You (Stronger)", is a song by American pop rock singer Kelly Clarkson. It was written by Jörgen Elofsson, Ali Tamposi, David Gamson, and Greg Kurstin; with Kurstin handling the production. It was sent to mainstream radio on January 17, 2012, by RCA Records as the second single from Clarkson's fifth album, Stronger (2011). The track is an uptempo pop rock song that uses a vibrant beat pulsating with synth and electric guitar. According to Clarkson, the song was inspired by a Friedrich Nietzsche quote, translated to "That which does not kill us makes us stronger", and its lyrics contain the theme of empowerment. The song has been received as an anthem for empowerment and recovery.
The song was met with positive reviews from music critics and became a commercial success worldwide. In the United States, it became Clarkson's third song to top the Billboard Hot 100 chart for three non-consecutive weeks, surpassing "A Moment Like This" and "My Life Would Suck Without You" as her longest-running number one single in the US. The song also topped the Billboard Hot Dance Club Songs, Adult Pop Songs, Pop Songs, and Adult Contemporary charts, making her the first artist ever to have topped the Hot 100 and each of Billboard's Dance/Club Play Songs, Country Songs, Adult Contemporary, Pop Songs, and Adult Pop Songs charts. Internationally, the song topped the charts in Poland and Slovakia and attained a top-ten position in over fifteen countries around the world. The song became Clarkson's first song to chart in Finland, and her second song to chart in France, following "Because of You". The song is currently her most commercially successful single in the United States, Denmark, Finland, New Zealand, Czech Republic, Hungary, Spain, Sweden, and the United Kingdom.
The song's accompanying music video was directed by Shane Drake. It incorporates the theme of a global flash mob. The music video garnered positive reception from critics who felt that its overall impact was exuberant. Clarkson has performed "Stronger (What Doesn't Kill You)" during several live appearances, notably during the first season of the American singing competition The X Factor, the 2011 VH1 Divas special, and on the 37th season of Saturday Night Live. Clarkson also included the song in the set list of her Stronger Tour.