The article tackles the exhibition work of Mies van der Rohe and Lilly Reich for the Barcelona International Exhibition of 1929. It reviews the beginnings of the pavilions, emerging in the 19th century and stresses the importance of this typology in the technological and structural evolution of modern architecture. Although most of these ephemeral constructions no longer exist or are replicas of the originals, such as the well-known Barcelona Pavilion, the text points out that they are an important part of 20th century architectural cultural legacy, and require conservation. Lastly, this concentrates on the German designs of Mies and Reich for the 1929 exhibition, projects which revolutionized the art of exhibiting and fostered the possibility of experimenting.