This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book focuses on the city as a sociocultural phenomenon, in particular as it developed since roughly the end of the Middle Ages in Western Europe. The present theory of urbanity deals with the historical origins and developments of Western European cities and their urban culture. The symbolic infrastructure of a city is its urban culture, its urbanity. In short, historically and sociologically we ought to distinguish between cities with and without a distinct urban culture, that is, urbanity. Urbanity was characterized by a narrow bond between the private and the public spheres of life. It was the worldview and ethos of the bourgeoisie as a socioeconomic class. Urbanity was a creative force that promoted and helped to institutionalize the sciences and the arts.