This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book presents case studies with the use of very different analytical lenses. It aims to compare European and non-European cities or address long-distance networks. The book addresses one city in particular include other scalar levels with a focus on social and intellectual networks, the circulation of concepts and of objects. The book also presents case studies which examine the relationships between knowledge and the city and how they changed in a period in which the nature and conception of both knowledge and the city transformed drastically. It focuses on Nicolaes Witsen, a mayor of Amsterdam in the late seventeenth-century Dutch Republic who could pre-eminently be seen as an actor prone to acting for the benefit of the city. In history of science, it is often assumed that knowledge production moved from cloisters and universities to the civic forum in the early modern period.