The article analyses citizen participation in urban and local public policies and projects. It points out that most participation systems, contrary to their intentions, lead to citizens' disengagement and even social fracture, because the design of participation does not take into consideration the social complexity of our cities. It also describes perverse mechanisms that are used to achieve the legitimisation of projects through direct participation, albeit minority, of the citizen sectors involved. The article concludes by stating that participation can be an excellent instrument of social cohesion if it is focused on identifying legitimate interests of different actors and sectors of the citizenship. And in an explicit, open, rigorous, and flexible approach to the development of policies that articulate different needs and interests around human and sustainable development objectives.