Reinhabitating means to stimulate a new attitude towards the use of dwellings and towards the necessity and nature of refurbishing, thinking about a new or different use or just about extending the life cycle of that commonly considered old. Reflecting on the use of our houses from this point of view, turns out to be especially suitable in the actual economical time of crisis, and notably in a country dealing with an oversized housing development. A newspaper’s new allows us to enlighten this situation. In 2004, more houses were built in Spain than altogether in Germany, France and Italy. In other words, a country with a population of 44 million inhabitants built more houses than three countries whose population comes altogether to 204 million inhabitants, almost five times the amount of Spain inhabitants. Under these circumstances and considering the high amount of empty dwellings, secondary residences, as well as unoccupied industrial and services facilities in good conditions, a research about new housing seems to be, nevertheless, a perfectly deferrable matter. More than a century ago it was published “The Practicon. Complete treatise on cooking and reusing the leftovers”. In that text Angel Muro, the author, defended a cuisine based on using the leftovers of meals and managing to cook with them delicious courses. We think that the house, its conception, its equipment and its form, remain buried by an avalanche of premises which always try to find an ideal house, as an impossible research. Perhaps studying the way of reinhabitating pre-existing houses, does not finally turn out to be just a naïve effort, but the most honest way to approach the actual housing situation while enabling an open-ended process of improvement. During 2009 and 2010 Habitar, a research group of the Catalan Polytechnic University, worked on this concept applied to the city of Madrid thanks to an I+D Research project granted by the Spanish Government, which concluded with the diffusion of the results by means of six exhibitions and nine small books. To take advantage of the leftovers of the Spanish opulence edge is the main aim of the present research, that pretend to assign a new use to preexistences. We do not refer to refurbishing or to interventions which pursue the renewal of a building, but to the proposal of modification of the use of the building itself. Reinhabitating does not mean restoring. Reinhabitating is reusing architecture, but just modifying the way of using it. It has not to do with plastic interventions, but with the how itself. In this article we will explain our experience with the popularization of these concepts which were applied to the house, to the street and to the city.