Modern architecture, which emerged in the twentieth century, is characterized by simplified forms and minimal ornamentation, significantly influenced by the Bauhaus School and the Modern Movement. The adoption of new materials such as steel and reinforced concrete, along with advanced technologies, revolutionized building design. In Spain, two approaches to modern architecture were developed: orthodox modernity, characterized by pure forms, and additive modernity, which combined traditional materials with modern concepts. Despite the Civil War and subsequent isolation, Spanish architecture progressed by integrating influences from the U.S. and Europe, with a strong focus on urban integration and environmental harmony. Engineers played a pivotal role in shaping modern architecture, overcoming technical limitations and expanding aesthetic possibilities through their collaboration with architects. To illustrate this, three notable examples from northern Spain are highlighted: the renovation of San Mamés Stadium (1953), the spatial roofs of the National Livestock Market of Torrelavega (1973), and the vaulted structures of the Señorío de Otazu winery (1997). These projects showcase the innovative use of materials, alongside advanced structural techniques like parabolic vaults and spatial roof designs. The collaboration between engineers and architects not only facilitated the creation of more functional, efficient, and sustainable buildings but also redefined architectural principles, advancing modern architecture significantly.