Passwords are crucial to our lives. They regulate our finances, protect our communications and prove who we are to others. They are powerful words. But from where did this equation of verbal knowledge with a person's identity emerge? What does it really mean, in the world of passwords, to say that one's "identity has been stolen"? What does the future of the password hold in store? In Password Martin Paul Eve traces the cultural histories of the password from ancient Rome and the "watchwords" of military encampments, through cultural representations (from Ali Baba to Harry Potter) and up to contemporary implementations in the digital world.