ATRII® is a contemporary art collective and association that investigates from a procedural and theoretical point of view the concept and physical space of the atrium or entrance hall. Invited artist analyse the idea of the atrium and design a series of procedural and dialectical works linking art to citizens and territories. ATRII® collaborates with other associations, private citizens, institutions, private companies and collectors, fostering relationships between the artists and building's inhabitants and users. The artist's research materials and projects are deposited in the Cittadella degli Archivi (Municipal Archives of the City of Milan). ATRII® Archivio Aperto is an atypical archive containing existing and hypothetical projects. It proposes as a new model for commissioning public artwork, intended as an important policy for local cultural and educational activities.