What motivates state, market, and civil society change agents to pursue the institutionalization of progressive planning practices, how do they do so, and why are they more or less effective in their pursuits? This dissertation, structured around three papers, uses interviews, focus groups, observation and documents to analyze how state and non-state actors in Medellin have sought to give progressive planning continuity. The first paper shows how the factors that account for institutionalization in weak institutional contexts must cover a range of eventualities, which I refer to as elements of institutionalization. Relations are needed to socialize a practice, create constituencies, mobilize interest, and provide enforcement. Practices reflect the public administration nature of state planning, thus highlighting the importance of reduced ambiguity, incentives to comply, resource allocation, and informational flows. Concepts help generate mental frameworks to cement the institution by providing justifications, substantiation, expectations, and influencing perception. Lastly, an acknowledgement of the importance of space is needed to target the appropriate scale, to ground concepts, to locate practices, and to situate relations. Identifying these elements provides a first contribution to the literature, and also evidences how fragile institutionalization efforts can be given the myriad of factors agents must attend to. The second paper shows that both state and non-state agents are aware of such fragility and thus attempt to create both formal and informal institutions. An analysis of the rationale for this pursuit and its mechanisms leads to the second contribution of this dissertation: the concept of institutional compounding. By impacting both formal and informal institutions, agents of change are better able to reduce the weaknesses associated with each; this however requires dynamically networking with individuals from at least one different societal category. As the elements and compounding contributions suggest, effectiveness in the pursuit of institutionalization is not easily assured. The third paper develops the argument that factors that enable experimentation or create critical junctures that allow new practices to emerge, such as decentralization, norm flexibility, and political initiative, can also represent impediments to institutionalization.