When was the last time you spoke to a stranger? In cities, we stand in silent buses and train carriages, ignoring each other. Online, we retreat into silos and carefully curate who we interact with. In our politics, we are increasingly consumed by a fear of people we've never met. But what if strangers, long believed to be the cause of our problems, were actually the solution? With the help of sociologists, psychologists, philosophers, political scientists and more, Joe Keohane sets out to investigate why we don't talk to strangers, and what happens when we do. From enhancing empathy, happiness and cognitive development to easing loneliness and isolation, passing encounters can root us in the world, deepening our sense of belonging.