The idea of ‘mind reading’ is ancient and has long been the province of magic and trickery rather than science. By 2050, advances in brain imaging technology and artificial intelligence will have made it possible to decode what people are experiencing and thinking. Not perfectly, but sufficiently to allow people (and machines) to look inside the previously inaccessible world of someone else’s consciousness. This will bring many benefits. In technology, advanced brain-computer interfacing will allow fluent interaction with our machine-dominated environment. In medicine, brain-damaged patients will have new means of communication, and new approaches to psychiatric disease may also follow. But the potential for brain-reading to lead to manipulation of peoples’ thoughts and behaviours will spark a new appreciation of the importance of privacy. Just as today we are learning that sharing everything on the internet comes at a price, ‘keeping our thoughts to ourselves’ will be something that we will have to learn how to do, to retain our status as individuals.