While in different fields of the arts1 – music, dance, scenic arts, or even visual or plastic arts – the idea of improvisation has been in use as a means to challenge the ideas of composition, of single authorship, and of the artwork as a product – which leads to the creation of alternative composition practices, processes, and procedures – in the field of urbanism, improvisation is still regarded as the opposite: the absence, or even the misconception, of any kind of planning. Taking the contemporary revaluation of the idea of improvisation in the arts as an example, this chapter seeks to deepen the understanding of that idea, and of improvisation itself as a practice, in order to dispute the supposed binary opposition between improvisation and urban planning (and urban design), proposing improvisation be considered as a principle that’s intrinsic to urban practices, processes, and procedures, especially ones that are more participatory, “informal,” and associated with grassroots self-construction, in order to grant more complexity to urban theory and practices through the idea of urban improvisations.2