Billion-Dollar Brain is a 1966 Cold War spy novel by Len Deighton. It was the fourth to feature an unnamed secret agent working for the British WOOC(P) intelligence agency. It follows The IPCRESS File (1962), Horse Under Water (1963), and Funeral in Berlin (1964). As in most of the author's novels, the plot of Billion-Dollar Brain (1967) is intricate, with many dead ends.