We propose to explore diverse scales of experimentation that contributed to the collective process of Medellín, from the critical years of the late 1980s up to now, with a special emphasis on the transformation process led during the past twenty years. We intend to analyze, synthesize and assess the results and progress achieved through two points of view that defined two different, but complementary scales of intervention; the large scale of urban and metropolitan planning and strategic projects, with decision making processes in terms of city planning and institutional interventions with strong impact, versus the intermediate and small scale of the Social Urbanism strategy in the most critical neighborhoods of the city, that use collaborative processes with the community to improve their everyday itinerary. Studying these roles of the urban project and their interdependence as a tool for different scales of urban management, the two voices present strategies as agents of change that strengthen agreements and shared visions, from citizen participation and democratic development. We hope to consolidate a critical reflection on the evolution of the city, which allows us to present lessons learned, prevalent challenges and good practices implemented in Medellin that can contribute to solve global issues of the contemporary city.