In contemporary debates about sustainable development, vernacular architecture plays an important role. Presenting itself as a dictionary of man’s constructive logic, it declares with no uncertainty its own usefulness, its connection to the soil, to the climate, the economy and technology. The capacity to incorporate change, to absorb the passing of time without losing the architectonical idea on which it lies, has made its forms intelligible and its language comprehensible to everybody. These qualities, together with the wide variety of forms that are found available within it, make vernacular architecture a reserve from which one can draw in order to stimulate creative thought upon a project. Despite vernacular architecture having been partially revalued, the role that it has played in the debate around ‘modernity’ and its contribution to the birth and development of modern architecture have been scarcely analysed and very much undervalued by both critics and historians. This thesis demonstrates the importance of the contribution made by vernacular architecture, investigating the architectural practice of some of the most renowned protagonists of architecture in the 20th century, among whom Mackintosh, Hoffmann, Loos, Le Corbusier, Sert, Aalto, Figini, Ponti, Rudofsky, Stirling, Abraham, the Smithsons, Venturi and Scott Brown. Furthermore, this thesis shows how some linguistic contaminations have been produced in the work of architects through their encounter with vernacular architecture during travels in native lands and abroad, and through the resulting theoretical reflections which have been documented in a large quantity of written material. For linguistic contamination I mean the analogous action undertaken by an element over another, on a morphological or semantic level. These actions are the result of a process that starts with the act of seeing, of observing and which matures in the thought put down on paper. For this reason I have decided to structure my thesis around the activities peculiar to architectural practice – seeing, thinking, projecting – to which the three sections of this thesis – travels, writings, projects – refer to. The first part demonstrates the importance of travel as a means to discover and gain direct knowledge of vernacular architecture and its legacy. For legacy I mean that baggage of impressions, sketches and photographs used by architects for reference in their future intellectual work. The second part highlights the existence of a large quantity of written material (articles, essays, books, conference papers) that witnesses the real and steady interest of modern ‘orthodox’ architects towards vernacular architecture. This section also considers the way in which some theoretical parameters of ‘modernity’ have been defined according to the observations contained in the written material. Finally, the third part shows the presence, in modern projects and works, of elements, structures, materials, and spatial and morphological devises that can be traced back to vernacular architecture, and that allow me to support the hypothesis of contaminations of vernacular architectural language on modern architectural language.