John Clayton Mayer ( MAY-ər; born October 16, 1977) is an American singer, songwriter, and guitarist. He attended Berklee College of Music in Boston, but he left for Atlanta in 1997 with fellow guitarist Clay Cook, with whom he formed the short-lived rock duo Lo-Fi Masters. After their split, Mayer continued to play at local clubs, refining his skills and gaining a minor following. He performed at the 2000 South by Southwest festival, and was subsequently signed by Aware Records, an imprint of Columbia Records through which he released his debut extended play (EP), Inside Wants Out (1999). His first two studio albums—Room for Squares (2001) and Heavier Things (2003)—were both met with critical and commercial success. The former album spawned the single "Your Body Is a Wonderland", which won Best Male Pop Vocal Performance at the 45th Annual Grammy Awards, while the latter album peaked atop the Billboard 200.

By 2005, Mayer had moved away from the acoustic music that characterized his early records, and further delved into the blues and rock music that had originally influenced him. Forming the John Mayer Trio, he released the live album Try! (2005) and his third studio album, Continuum (2006). The latter was met with positive critical reception and was nominated for Album of the Year, and won both Best Pop Vocal Album and Best Male Pop Vocal Performance for its single "Waiting on the World to Change" at the 49th Annual Grammy Awards. It was followed by Battle Studies (2009), which marked his return to pop.

After having several controversial incidents with the media, Mayer withdrew from public life in 2010 and drew inspiration from the 1970s pop music of Laurel Canyon for the sound of his fifth studio album, Born and Raised (2012). Discovery of a granuloma on his vocal cords delayed the release of the album until May 2012, and forced him to cancel its accompanying tour. Despite favorable reception and becoming his second release to peak atop the Billboard 200, the album was less commercially successful than his previous work. Mayer recovered in January 2013 and released his sixth studio album, Paradise Valley in August of that year, which peaked at number two on the chart and incorporated country, folk, and Americana influences. His seventh album, The Search for Everything (2017) was a loose concept album based around themes of a romantic break-up. His eighth, Sob Rock (2021), was inspired by 1980s soft rock music. In 2023, Rolling Stone ranked Mayer at number 61 on "The 250 Greatest Guitarists of All Time" list.

Outside of his solo career, Mayer has produced and provided music for various artists spanning multiple genres, such as Frank Ocean, Kanye West, Travis Scott, Alicia Keys, Jack Harlow, Ed Sheeran, Shawn Mendes, Harry Styles, Daniel Caesar, Khalid, Jhené Aiko, and Barbra Streisand, among others. In 2015, three former members of the Grateful Dead joined with Mayer and two other musicians to form the band Dead & Company. It was the latest of several reunions of the band's surviving members since Jerry Garcia's death in 1995. Mayer's secondary career pursuits extend to television hosting, comedy, and writing; he has authored columns for magazines such as Esquire. He supports various causes and has performed at charity benefits. He is a watch aficionado (with a collection he values in the "tens of millions" of dollars), contributing to the watch site Hodinkee, has been on the jury at the Grand Prix d'Horlogerie de Genève, and was appointed as the Creative Conduit of Audemars Piguet in 2024. By 2014, he had sold a total of over 20 million albums worldwide.