The idea—the possibility—of reading the mind, from the outside or indeed even from the inside, has exercised humanity from the earliest times. If we could read other minds both prospectively, to discern intentions and plans, and retrospectively, to discover what had been “on” those minds when various events had occurred, the implications for morality and for law and social policy would be immense. Recent advances in neuroscience have offered some, probably remote, prospects of improved access to the mind, but a different branch of technology seems to offer the most promising and the most daunting prospect for both mind reading and mind misreading. You can’t have the possibility of the one without the possibility of the other. This article tells some of this story.