cities and suburbs to the opportunities we have to casually interact with strangers, friends, and neighbors. It is especially important for children, the elderly, and other people whose limited mobility or lack of autonomy binds them to the places where they live. But social infrastructure affects everyone. And while social infrastructure alone isn't sufficient to unite polarized societies, protect vulnerable communities, or connect alienated individuals, we can't address these challenges without it. In this book, I'll explain how and why.