In urban regeneration, trial-and-error methods can be adopted to minimize the risk of failure and the unintended negative effects that often accompany “top-down” projects. Over the past decade in France, the transitional reuse has entered urban planners, designers and city makers’ toolkit. Through dedicated methodological approaches and the involvement of local communities, they test alternative uses for underutilised spaces and buildings, aiming to identify sustainable long-term functions. This distinctly “design-oriented” approach should not be reduced to the concept of temporary or “meanwhile” uses. It is not merely about activating empty spaces while awaiting decisions on their future, but rather about shaping these decisions by exploring alternative scenarios. This is the method adopted by KCity consultancy in its urban regeneration practices. As referred in the paper, transitional urbanism translates into action the idea of urban regeneration as a process. Unleashing the potential of experimental approaches should enable their integration into urban planning. Transitional urbanism is a practice aimed at revealing the unexpected, creating opportunities for the informality that is often missing from traditional planning. Emphasising the interest of trial-and-error methods, we point out that experimentation does not mean improvisation; rather, it demands skills, technical expertise, and a reflective approach. This defines a potential avenue for the renewal of professional practices.