As an object of research in general, and in the spatial planning field in particular, 'institutional innovation' is a relatively recent focus of investigation, but more and more considered by scholars aiming at understanding how decision-makers in organizations and spatial planners in cities can adapt their approaches to cope with a world molded by uncertainties, societal challenges and structural mutations. Specifically, as highlighted in this introductory paper and illustrated in various forms in the present Special issue, institutional innovation is a crucial key to urban transformation and territorial resilience. As core players for adapting territorial development strategies, urban planners, along with economic, social and political local actors, are also decisive in changing the 'rules of the game' and initiating new behavioral patterns and collective arrangements, i.e. in favoring 'institutional innovations' that can contribute to an urban transformation adapted to the new challenges and constraints cities must face. Still, institutional innovations in spatial planning are subject to many conditional factors and brakes that can inhibit their potential impact, or even make them unlikely to be initiated and implemented. As shown, it is here where open attitude towards experiments, learning and creativity play a decisive role in changing the institutional levers for innovative approaches and practices in the urban field.