For millennia people have held folk beliefs about the existence of the doppelganger--"double walker" in German--a look-alike second self that is often the antithesis of one's identity and is usually considered an omen of misfortune or death. The theme of the double has inspired works by E.T.A. Hoffmann, Poe, de Maupassant, Dostoevsky and others, and has been the basis for many classic mystery, horror and science fiction movies. This critical survey examines the double in more than 100 films by such acclaimed directors as Alfred Hitchcock, Mario Bava, Roger Corman, David Cronenberg, George Romero, Fritz Lang, James Cameron, Robert Siodmak, Don Siegel, John Frankenheimer, Terry Gilliam, Brian De Palma and Roman Polanski.