Halfway between the inside and outside, in direct contact with the human flow of modern metropolis, throughout the twentieth century commercial displays offer a unique look into the European avant-garde architectural expressions, anticipating concepts that will be further incorporated into the architecture of large scale. The main focus of the current analysis is on Madrid, and the development that window displays experimented from the mid-nineteenth century, when the traditional stores needed to manage the effect of change of paradigm in selling strategies. The store would be no longer a place for manufacturing, but for selling exclusively. At the very beginning the reputation of local craftsmen was enough to attract their clients. In many stores the type of merchandise that was sold inside was not even showed at their fronts, as the popular saying goes, ´good wine needs no bush´(´O bom pano na arca de vende´). Then the huge development of manufactured merchandise brought about by the Industrial Revolution, made better products available for everyone on different shops. Proto-marketing was born, and traders were encouraged to improve the efficiency of their shop displays in order to attract as many people as possible, developing new design concepts following the historicist trend of the times, but making them compatible with the rapid assimilation of the latest in glass, metal and lighting technologies. It was not until the 1920s that Spanish architects started to get in touch with the principles of modernity. In Madrid, the new Gran Vía had recently become the symbol of the economic and social development in Spain after the First World War. The first implementation phase of this new urban stage had just been finished and, although it was the unquestionable proof that historical eclecticism style was at its height, a whole collective of young architects, ‘generation of 25’ (Zuazo, García Mercadal, Arniches and Domínguez, Feduchi, Bergamín, Gutiérrez Soto, …), could find at the ground level of its neo-classicist buildings the seeds of the emerging modernity. Here they found a whole collection of shops, cafes and bars, whose display windows and luminous signs had been working for many years with the same principles defended by the new European avant-garde styles of the moment, from the functionalist rationalism to the expressionism, which these young architects were beginning to study through international publications and their travels around Europe. In 1925, their visit to the International Decorative Arts and Modern Industries Exhibition of Paris became the confirmation of their first theoretical intuition and the catalyst for its implementation through their earlier works back to Madrid. Shop windows, cinemas and cocktail bars became almost immediately the test for these attitudes, which would raise a clear response to the new metropolis was demanding new uses without established traditional models, which allowed the incorporation of the new logic of modern language. The Spanish Civil War radically truncated this trend, which in 1935 had reached its apogee. After the war, the pursuit of the ‘national style’ advocated by the victorious dictatorial regime, forced to return to the old regionalist historicism, which was followed by all the authors who remained active. However, at the end of the forties, a new batch of newly qualified architects, who would collect the inheritance of the generation of 25, started the first reaction to the official imposition. Through their early works in commercial interior design, many of the artists today deemed the masters of contemporary Spanish architecture, as Carvajal, Blanco Soler, De la Sota, Corrales and Molezún or Fisac, initiated the recovery of the forgotten modernity, through a new functionalism of American consumerist influence, translating the concept of the Le Corbusier’s ‘machine for living’ into the ‘selling machine’, where the window display was erected as the crucial piece of design.