Mark Ellis (born 16 August 1960), known by his professional pseudonym Flood, is a British post-punk and alternative rock record producer and audio engineer. Flood's list of work includes projects with New Order, U2, Nine Inch Nails, Marc and the Mambas, Depeche Mode, Gary Numan, King, Ministry, The Charlatans, Thirty Seconds to Mars, Erasure, Nick Cave and the Bad Seeds, PJ Harvey, Foals, a-ha, Orbital, Sigur Rós, The Smashing Pumpkins, The Killers, White Lies, Pop Will Eat Itself, Warpaint and EOB. His co-production collaborations have included projects with Brian Eno, Daniel Lanois, Steve Lillywhite, and longtime collaborator Alan Moulder, with whom he co-founded the Assault & Battery studio complex. In 2006, his work with U2 led to his sharing of the Grammy Award for Album of the Year for How to Dismantle an Atomic Bomb.
He is not to be confused with Mark Ellis, the bassist from the British mod revival band The Lambrettas from the late 1970s and early 1980s.