This paper puts forward a reflection on the ambit of urban conservation by taking patina as the object of discussion. Patina is understood as the effect left by the passage of time on the exterior surfaces of urban elements and on social practices. Patina is important for the perception of the age value because it points to the perception of the passage of through the idea of ageing and decay. In the first instance, the article traces one evolution of the concept, beginning with the physical-chemical plane, as patina is both an action and an effect caused in paint and metals, and leads on to a critical approach , given that patina results in alterations in the object, the treatment of which will be conditioned by the values which it aggregates. The second section sets forth a broadening of the concept, and reaches the understanding that patina is manifested in the city in two dimensions – the physical-material one and the immaterial one – and on two scales – that of the city and that of place. Finally, the third section discusses the possibilities of treating the patina in the processes of urban revitalization, based on the notions of permanence and transformation, continuous actions and episodic actions. The understanding is reached that as a result of the regeneration capacity of the patina; it is a sine qua non that the actions of urban revitalization and rehabilitation take this into account when seeking to maintain the equilibrium of modifications. Therefore, when interventions are made in old areas, the patina of which has become an inherent part of their identity, the attempt should be made to grade the transformations in time, inevitably so for contemporary uses, in such a way that the patina may regenerate itself on the old surfaces and re-emerge on the surface of the new elements.