Density functional theory is one of the most widely used yet contentious issues in science, and yet many people will never even have heard about it. We discuss its origins, successes and controversies and talk to Professor Fred Manby, from the University of Bristol, who both uses and develops DFT in his research.Credits:- Support: TMCS, EPSRC- Theme music: from "Earnest's Understanding" © 2017 Charles Ormrod