Around 1900, the European city faced a range of serious problems, in particular with respect to urban planning and hygiene. The search for best practices in other urban spaces, also labeled transnational municipalism, promised solutions. This volume combines approaches from urban history with the idea of knowledge in transit as developed in the history of science. The first part of the introduction introduces the main theoretical concepts of the book. It emphasizes that this applied urban knowledge was mediated through interurban networks and appropriated in new and creative ways by cities in Eastern and Southern Europe. This approach serves to overcome outdated ideas of center and periphery, and shows that cities such as Budapest, Barcelona and Lemberg represent variants of modernity rather than “backwardness.” The second part of the introduction addresses the common themes connecting the 12 chapters of the book. This includes the multi-directionality of exchanges between urban spaces, the strong connections between urban planning and the rising nationalism of the late nineteenth century, the tensions between universal models and local resistance to urban modernization, and the role (inter-)urban actors played in the circulation of knowledge and practices.