This dissertation investigates the transnational circulation of city planning knowledge from the early 1890s to the outbreak of the First World War in 1914. Using the professional trajectory of Swedish architect and city planner Per Olof Hallman (1869–1941) as an analytical entry point, the study adopts a transnational microhistorical approach, situating Hallman within a wider cohort of Swedish practitioners, including Fredrik Sundbärg (1860–1913), Albert Lilienberg (1879–1967), Nils Gellerstedt (1875–1961), and Anders Nilsson (1844–1936). Together, this cohort formed a transitional generation that moved away from rigid geometric street grids, integrating instead topographically adapted and artistically grounded principles drawn from German Städtebau and British decentralist models. The thesis examines four distinct mechanisms of knowledge mobility. First, it considers study tours, particularly Hallman’s 1895 trip around Europe, as early examples of active translation, where foreign practices were observed and adopted. Second, it analyses early planning competitions in Helsinki- Töölö and Gothenburg, showing how they functioned as structured arenas for debating international planning ideas. Third, it investigates international exhibitions in Dresden, Berlin, and London as semi-curated spaces where visual communication facilitated cross-border learning. Finally, it maps the informal professional networks that supported the sustained circulation of ideas within the Nordic region and beyond. Ultimately, the research shows that the physical and institutional realities of the modern Swedish city resulted from active transnational translation. Local agents challenged path-dependent administrative practices, such as the 1874 Building Ordinance, paving the way for municipal land acquisitions and the 1907 Town Planning Act. By utilising these four mechanisms, early Swedish city planners actively filtered and negotiated foreign models to reshape their own urban environments.