Jonathan Richard Guy Greenwood (born 5 November 1971) is an English musician. He is the lead guitarist and keyboardist of the rock band Radiohead, and has composed numerous film scores. He has been named one of the greatest guitarists by numerous publications, including Rolling Stone.

Along with his elder brother, Colin, Greenwood attended Abingdon School in Abingdon near Oxford, where he formed Radiohead. Their debut single, "Creep" (1992), was distinguished by Greenwood's aggressive guitar work. Radiohead have achieved acclaim and sold more than 30 million albums. He was inducted into the Rock and Roll Hall of Fame as a member of Radiohead in 2019.

Greenwood is a multi-instrumentalist and a prominent player of the ondes Martenot, an early electronic instrument. He uses electronic techniques such as programming, sampling and looping, and writes music software. He described his role in Radiohead as an arranger, helping transform Thom Yorke's demos into finished songs. The only classically trained member of Radiohead, Greenwood has composed for orchestras including the London Contemporary Orchestra and the BBC Concert Orchestra, and his arrangements feature on Radiohead records.

Greenwood released his first solo work, the soundtrack for the film Bodysong, in 2003. In 2007, he scored There Will Be Blood, the first of several collaborations with the director Paul Thomas Anderson. In 2018, he was nominated for an Academy Award for his score for Anderson's Phantom Thread. He was nominated again for his score for The Power of the Dog (2021), directed by Jane Campion. Greenwood also scored the Lynne Ramsay films We Need to Talk About Kevin (2011) and You Were Never Really Here (2017). He has collaborated with Middle Eastern musicians including the Israeli songwriters Shye Ben Tzur and Dudu Tassa. In 2021, Greenwood debuted a new band, the Smile, with Yorke and the drummer Tom Skinner.