Jonathan Richard Guy "Jonny" Greenwood (born 5 November 1971) is an English musician and composer best known as a member of the rock band Radiohead. Beyond his primary roles as Radiohead's lead guitarist and keyboardist, Greenwood is a multi-instrumentalist and also plays viola, harmonica, glockenspiel, ondes Martenot, banjo and drums, and works with computer-generated sounds and sampling; he is also a computer programmer and writes music software used by Radiohead. Noted for his aggressive playing style, Greenwood is consistently named as one of the greatest guitarists of all time.

Greenwood composed the soundtracks for the films Bodysong (2003), There Will Be Blood (2007), Norwegian Wood (2010), We Need To Talk About Kevin (2011), The Master (2012) and Inherent Vice(2014), and serves as composer-in-residence for the BBC Concert Orchestra. He is the younger brother of Radiohead bassist Colin Greenwood.