Alvar Aalto created innovative architecture in his breakthrough work, Paimio Sanatorium, located in Southwestern Finland and designed between 1928 and 1933. This empirical case study looked at the iconic piece of architecture from a new angle by implementing the actor-network theory (ANT). The focus was on how the architecture of the sanatorium came to be. A detailed description of the chronology and administration of the building process enabled observing on the role of the agency of the architect. The study surveyed the cooperation, collaboration, and decision making of the agency during the construction period. The first part of this paper focused on the relations and conditions of producing the sanatorium and analyzed the building through drawings and archive material; the second part linked to the actor-network theory of Bruno Latour and included a discussion on how Aalto managed to bring along the other actors. The study clearly showed the importance of a collaborative effort in a building project. The most special architectural solutions for Paimio Sanatorium, a demanding institutional building project, came into being in circumstances where the architect managed to create a viable network that merged collective competence with material factors.