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Exploring a discipline like improvisation in jazz makes it possible to show the structuring knowledge that positions this improvisation at the crossroads between an artistic form relying on memory and one based on hope. The improviser is constantly concerned with both listening attentively and letting him or herself go, between the mastering of an already existing work and its repetition, and the tensions that exist with new creations. It is also possible to observe collective organizational forms that put into practice a form of “diagonal” management that opens up opportunities to redefine the role of the orchestra director. By examining the interaction of knowledge of improvisation and that of development and planning, which in theory resists the idea of improvisation, this article examines the characteristics that enable improvisation to be seen as a new source of meaning and legitimacy for urban planners. Analyzing different emblematic forms of improvisation opens up new ways of reflecting on these questions.