City dwellers and public policies are today confronted with global urbanization, the complexity of cities, and the increased climate risks. Consequently, architects and urban planners constantly renew their practices and initiate collaborative approaches involving other stakeholders in the territory. They are invited to design new urban forms and urban production to best respond to these socio-urban issues and challenges. If the implementation of participatory approaches is emerging, prospective design and the participative design approach takes a strategic place. Above all, it is a question of thinking together about the scales of territorial change to respond to the social and urbanistic challenges of tomorrow, while taking into account the diversity of populations and cultures. From then on, the critical and speculative design brings a unique reflective, innovative and experiential dimension to designing futures. The participative approach involves a dynamic of co-production between all the actors of the territory to create scenarios that stimulate the imagination and propose courses of action and engagement. Based on a theoretical and operational analysis this contribution demonstrates how critical and speculative design takes part in a co-production process for territories and participates at the same time in the renewal methods of analysis and the production of the territory by architects and urban planners. Case studies using a methodological tool called ‘frieze for territorial futures’ illustrate this contribution.