The scientific discoveries of recent decades and in particular those relating to Complexity Theory have led to recognize the city as a typical example of adaptive complex system. Urban and architectural design must face today this complexity and the substantial unpredictability of generative bottom-up processes that determine it. That is, design should be aimed not to produce a finished object but rather to trigger a processuality that welcomes and benefits from the creativity of the community that the project itself will host. A design, therefore, no longer prescriptive but aimed at orienting the spontaneous evolution of the city system. This means, above all, stop thinking about architecture as an immutable finished object and start to consider it as a continuous process, that is, to adopt a procedural thinking. This finds its best expression in programming languages that today seem the most effective tools to manage a design process leading to not a single outcome, but all possible outcomes.