Explore the fascinating world of inner voices in this Royal Institution lecture by psychologist Charles Fernyhough. Delve into the vital role inner speech plays in our thinking processes, from childhood development to individuals who hear voices. Learn about expanded and condensed speech, private speech, and the challenges of studying inner experiences. Discover the historical context of inner dialogue through examples like Marjorie Kemp and Julian of Norwich. Examine the connection between inner speech and theory of mind, as well as its implications for brain development. Gain insights into current research methodologies, including smartphone apps and descriptive experience sampling, and consider future directions in this intriguing field of study.